qid int64 2 112k | question stringlengths 61 6.7k | positives listlengths 1 1 | negatives listlengths 1 10 |
|---|---|---|---|
60,706 | <p>I know most creatures take time to learn some things.</p>
<ul>
<li><p>Birds take some time to fly.</p></li>
<li><p>Human beings take some time walk or stand.</p></li>
</ul>
<p>But in the case of the deer species, it's different. It can stand the same day it's born. Why is this so? </p>
| [
{
"answer_id": 60707,
"pm_score": 7,
"text": "<p>If you compare placental mammals in how much time they need to start walking, you'll see that deer are no exception. Humans are an exception.</p>\n\n<p><strong>Hypothesis of Obstetrical Dilemma</strong></p>\n\n<p>The hypothesis of Obstetrical Dilemma stat... | [
{
"answer_id": 60711,
"pm_score": 5,
"text": "<p>Deer are hardly unique in this, The young of horses, cows, and I suspect most grazing species are able to walk soon after birth. The reason, of course, is evolutionary: flight is the species mechanism for avoiding predators, so if they weren't able to f... |
62,579 | <p>Are there known life forms that are able to transform mechanical energy into chemical energy?</p>
<p><a href="https://biology.stackexchange.com/q/37063/21">This</a> question asks a similar subject, but more specific and has no answers.</p>
<p>The background of this question are thoughts about hypothetical life on tidally locked exoplanets of red dwarf stars, where light for photosynthesis is scarce but mechanical energy (storms and/or water currents) aplenty. </p>
| [
{
"answer_id": 62616,
"pm_score": 4,
"text": "<p>There are no known life forms that use mechanical energy as a primary form of metabolic energy (i.e., for generic cellular functions). Many life forms are sensitive to mechanical disruption in some way, so they do utilize mechanical energy, but in a very ... | [
{
"answer_id": 62608,
"pm_score": 0,
"text": "<p>I did read and article about some bacterial spores being used to generate electricity as they expand and contract. Not sure if that is a relevant answer but that's what came to mind when I read your question. <a href=\"https://www.sciencedaily.com/release... |
64,822 | <p>I was drinking a glass of milk the other day and that got me thinking that no other animal to my knowledge drinks milk past their infant stages. One could argue that cats might but it isn't good for them to do.</p>
<p><strong>Are humans the only animal that are able to drink milk as adults and not have it cause issues?</strong></p>
<p>Of course, I know some people do have lactose intolerance too.</p>
| [
{
"answer_id": 64824,
"pm_score": 7,
"text": "<p>Good observation!</p>\n<h1>Gene coding for the lactase</h1>\n<p><strong>Gene LCT</strong></p>\n<p>Mammals have a gene (called <code>LCT C/T-13910</code>) coding for the <a href=\"https://en.wikipedia.org/wiki/Lactase\" rel=\"noreferrer\">lactase</a> enzym... | [
{
"answer_id": 64831,
"pm_score": 5,
"text": "<p>Just to point out an exception, <a href=\"http://www.dairyfarmguide.com/inter-sucking-or-self-sucking-0161.html\" rel=\"noreferrer\">adult cows sucking other cows' milk are not uncommon</a>. At least, it's common enough to be a concern in dairy farms and ... |
67,494 | <p>I've heard the argument from a lot of creationists that all the evidence for natural selection (and by extension, evolution) in general is worthless because natural selection is so flexible that it could cover all the data, no matter what we discovered. In essence, that natural selection is a tautology:</p>
<blockquote>
<p>Survival of the fittest. What is 'fit'? What survives.</p>
</blockquote>
<p>There are other creationists, however, that admit that natural selection could be falsified. These are split into two groups:</p>
<ul>
<li>The ones that say, if you rephrase natural selection as a non-tautology, it becomes obvious that it doesn't work:</li>
</ul>
<blockquote>
<p>Natural selection has been criticized as a tautology. This would be a major problem for evolutionary biology, if true, because tautological statements can't be falsified and, therefore, can't be scientific. There is merit to this critique insofar as the theory of natural selection is indeed generally described in a tautological manner. However, natural selection can be described non-tautologically if we’re careful. Natural selection should be defined as the theory that attempts to predict and retrodict evolutionary change through environmental forces acting upon organisms. However, this re-framing comes at a cost: it reveals, based on our current knowledge of evolutionary forces, the lack of ability to make accurate predictions about expected changes except in the most simple of circumstances.</p>
</blockquote>
<ul>
<li>And those that say that the falsifying options provided by natural science are impossible to actually use. Here are some of those falsifying options:</li>
</ul>
<blockquote>
<ol>
<li>Charles Darwin himself proposed a rather strong test of evolution: "If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down." [Darwin1859, pg. 175]. This is the basis of claims by various intelligent design writers that various biological structures, such as the vertebrate immune system or the bacterial flagellum, are "irreducibly complex" -- they consist of multiple components that could not develop in the absence of the others. However, these structures have been exhaustively studied in the scientific literature, and scientists have demonstrated entirely plausible evolutionary pathways. See Complexity.</li>
</ol>
</blockquote>
<ol>
<li>Famed biologist J. B. S. Haldane, when asked what evidence could disprove evolution, mentioned "fossil rabbits in the Precambrian era" [Ridley2004, pg. 66]. This is because mammals, according to current scientific analysis, did not emerge until approximately 40 million years ago, whereas the Precambrian era is prior to approximately 570 million years, when only the most primitive organisms existed on earth.</li>
<li>Biologists had long conjectured that human chromosome number two was the result of a fusion of two corresponding chromosomes in most other primates. If DNA analysis of these chromosomes had shown that this was not the case, then modern evolutionary theory would indeed be drawn into question. This "fusion hypothesis" was indeed confirmed, rather dramatically, in 1993 (and further in 2005), by the identification of the exact point of fusion. For additional details see DNA.</li>
<li>Modern DNA sequencing technology has provided a rigorous test of evolution, far beyond the wildest dreams of Charles Darwin. In particular, comparison of DNA sequences between organisms can be used as a measure of relatedness, and can further be used to actually construct the most likely "family tree" hierarchical relationship between a set of organisms. Such analyses have been done, and the results so far dramatically confirm the family tree that had been earlier constructed solely based on comparisons of body structure and biochemistry. For additional details see DNA.</li>
</ol>
<p>Is there any way to save natural selection? To do so, we need to:</p>
<ul>
<li>Prove it can be explained non-tautologically</li>
<li>Prove that it does make useful predictions</li>
<li>Give falsifying experiments that are reproducable and actually possible.</li>
</ul>
| [
{
"answer_id": 67502,
"pm_score": 5,
"text": "<p>I think @Remi.b's answer is great and really the only way to answer your questions is with a comprehensive introduction to evolution. However, I wanted to address the tautology issue more directly.</p>\n\n<p>First, the \"survival of the fittest\" seems li... | [
{
"answer_id": 67499,
"pm_score": 4,
"text": "<p><strong>The tautology argument is an attack on a rare phrasing and not on the nature of the theory of evolution.</strong></p>\n<p>First, the theory of evolution is way more than just natural selection but let's ignore that for the moment.</p>\n<p>The phra... |
69,304 | <p>I've always wondered why cells have only one nucleus, as having multiple would seemingly prevent mutation. Are there examples of organisms with multiple nucleuses? If not, is there a reason?</p>
| [
{
"answer_id": 69307,
"pm_score": 6,
"text": "<blockquote>\n <p>Are there examples of cells with more than one nucleus?</p>\n</blockquote>\n\n<p>Yes, they are called <a href=\"https://en.wikipedia.org/wiki/Multinucleate\" rel=\"nofollow noreferrer\">Multinucleate cells</a>. There are two types of multi... | [
{
"answer_id": 69308,
"pm_score": 3,
"text": "<p>According to this article <a href=\"https://www.newscientist.com/article/dn20191-zoologger-the-hairy-beast-with-seven-fuzzy-sexes/\" rel=\"nofollow noreferrer\">The hairy beast with seven fuzzy sexes</a></p>\n\n<p><em>Tetrahymena thermophila</em> has two:... |
71,259 | <p>If you take two computer programs and randomly swapped pieces from each of them. The result is not going to work. It will just be garbage. If you take two novels and randomly swapped chapters the result will be garbage too. </p>
<p>How is it than DNA (which is infinitely more complicated) can be combined, some from the father and some from the mother and yet it still somehow works?</p>
<p>Can you give a simple example?</p>
| [
{
"answer_id": 71271,
"pm_score": 5,
"text": "<p>Homologous DNA recombination does not swap parts randomly in the sense that any two bits of DNA can swap places. DNA recombination is random in the sense that it may or may not occur. In fact DNA homologous recombination is highly specific and its specifi... | [
{
"answer_id": 71260,
"pm_score": 5,
"text": "<p>One must always be careful not to stretch an analogy further than it can withstand, but since you started these analogies, I will follow up on them and explain the small mistake you've done in their representations.</p>\n\n<p>The two books are not as diff... |
71,273 | <p>Are there other species that get nosebleeds? If so, do they occur for the same reasons that humans get nosebleeds? How would an animal stop a nosebleed?</p>
| [
{
"answer_id": 71271,
"pm_score": 5,
"text": "<p>Homologous DNA recombination does not swap parts randomly in the sense that any two bits of DNA can swap places. DNA recombination is random in the sense that it may or may not occur. In fact DNA homologous recombination is highly specific and its specifi... | [
{
"answer_id": 71260,
"pm_score": 5,
"text": "<p>One must always be careful not to stretch an analogy further than it can withstand, but since you started these analogies, I will follow up on them and explain the small mistake you've done in their representations.</p>\n\n<p>The two books are not as diff... |
72,388 | <p>I'm currently in the middle of writing a story, and one of the story elements threw up a question for me. In this story, there are two siblings, who are only one or two months apart in age. As they grow older, they start to question how this age difference is even possible. How could their mother have had <em>another</em> child after just a month of giving birth to the first child? They suspect that they're not related and don't actually have the same mother, and it turns out that it's true.</p>
<p>I want to know if that suspicion is justified. I began to think of ways two siblings can be less than the usual nine months apart in age and yet still be related to each other. One idea I had was of twins, one of whom is born earlier, while the other had to stay inside the womb for another month for whatever medical reason.</p>
<p>Basically, my question is: can you have siblings (with the same mother and father), who are less than nine months apart in age? And if yes, how?</p>
| [
{
"answer_id": 72390,
"pm_score": 7,
"text": "<p><strong>What do you mean by siblings?</strong></p>\n\n<p>If by siblings, you accept cases of individuals having the same father but not the same mother, then of course, it is possible! Below, I will assume you are referring to full siblings (eventually tw... | [
{
"answer_id": 72398,
"pm_score": 5,
"text": "<p>Yes, this can happen in non-twins. There is a rare phenomenon that can occur in humans (and some other animals), called '<strong>Superfetation</strong>'. This is when some time during pregnancy, a woman has a second oocyte fertilized and implanted. This e... |
74,887 | <p>Typically, people call viruses some kind of organic compounds that cannot reproduce autonomously and which <strong>lower the fitness</strong> of their hosts. Even the word "virus" means "venom" in Latin.</p>
<p>But from the perspective of natural selection, one would expect those organic compounds that cannot reproduce autonomously, but which would increase the fitness of their hosts, to be more widespread. One can see an analogy with bacteria: people are more aware of harmful bacteria and even such words as "microbe" are perceived as somewhat harmful (among non-biologists for sure). But we know that an animal body contains many more useful bacteria than harmful ones, and animals have their own microflora, which are necessary for survival.</p>
<p>The same must be true for viruses: those viruses which were useful (or at least unharmful) to their hosts would be passed more easily to other organisms since their hosts would have a selective advantage.</p>
<p>So, do such beneficial for their direct hosts viruses exist? If so, what are they called? What are the examples?</p>
| [
{
"answer_id": 74896,
"pm_score": 7,
"text": "<p>Do they exist? Yes</p>\n\n<p>What are they called? Marilyn Roossinck calls them viral mutualistic symbiotes. She has an excellent review <a href=\"https://www.nature.com/articles/nrmicro2491\" rel=\"noreferrer\">here</a>. </p>\n\n<p>What are some examples... | [
{
"answer_id": 74899,
"pm_score": 5,
"text": "<p>Another good virus would be a <a href=\"https://en.wikipedia.org/wiki/Bacteriophage\" rel=\"noreferrer\"><em>Bacteriophage</em></a>, a virus that infects and kills illness-causing bacteria. From Wiki:</p>\n<blockquote>\n<p>A bacteriophage also known info... |
76,455 | <p>Humans have a huge variation in physical ability because of exercise differences. Olympic athletes are a number of times stronger than average people on the street. It seems that variation in animals is very small, but I am wondering if one could force an animal to follow a specific program and eat specific food to get a lot stronger, agile, etc. than an average animal of the same species.</p>
| [
{
"answer_id": 76457,
"pm_score": 5,
"text": "<p>When I visited the <a href=\"http://www.cheetah.co.za/default.html\" rel=\"noreferrer\">Cheetah Outreach Center</a> in South Africa, the guides there told us that their captive cheetahs couldn't run nearly as fast as wild ones, and that wild ones were muc... | [
{
"answer_id": 76456,
"pm_score": 4,
"text": "<blockquote>\n <p>Can animals train to be noticeably stronger, faster, more agile.. than other animals of the same species?</p>\n</blockquote>\n\n<p>Yes, of course!</p>\n\n<p>Humans are animals, so yes! But even in non-human animals. You can look for exampl... |
77,329 | <p>Analysing the transcriptome (RNA-Seq, microarrays, qPCR etc) is probably the most widely used technology to assess gene expression and dynamic cellular processes. The results are then extrapolated (functional analyses, GO etc) to infer biological cellular consequences. RNAs are really only the middle-man. Presence of an mRNA doesn't necessarily mean that it will become a protein. It could be degraded by microRNAs etc. before translation. It is eventually the protein that are actually causal to a biological change.</p>
<p>So, my question is why not just go directly to the proteins. Why not just extract the proteins and sequence them, quantify them, analyse and draw conclusions? What are the compelling arguments to study the transcriptome to understand biological processes?</p>
| [
{
"answer_id": 77367,
"pm_score": 3,
"text": "<blockquote>\n <p>Q: Why not just extract the proteins…</p>\n</blockquote>\n\n<p>A: It’s not just a question of <em>extracting</em> the proteins, you would need to <em>separate</em> them and then <em>isolate</em> each of them. There is currently no practica... | [
{
"answer_id": 77331,
"pm_score": 2,
"text": "<p>While you are correct that 'the end output' is always protein and that functional analysis on the mRNA level can ignore things translational control, there good reasons to analyse the transcriptome:</p>\n\n<p>1) Like you said a lot can happen with mRNA: i... |
77,587 | <p>I am trying to make a point to someone that just because two plants share a family and one plant is safe for human consumption, it does not follow that the other plant also is safe for human consumption. Can anyone provide an example I can use as proof?</p>
| [
{
"answer_id": 77591,
"pm_score": 7,
"text": "<p>The most classic example if you want to win this argument would be the family <a href=\"https://en.wikipedia.org/wiki/Solanaceae\" rel=\"noreferrer\">Solanaceae</a>.</p>\n\n<p>Also referred to as the Nightshade family, it includes the <a href=\"https://en... | [
{
"answer_id": 77594,
"pm_score": 5,
"text": "<p>Both the <a href=\"https://en.wikipedia.org/wiki/Cashew\" rel=\"noreferrer\">cashew</a> and <a href=\"https://en.wikipedia.org/wiki/Toxicodendron_radicans\" rel=\"noreferrer\">poison ivy</a> are members of the <a href=\"https://en.wikipedia.org/wiki/Anaca... |
92,356 | <p>I am curious if there has ever been a (modern) clinical study where a healthy volunteer was purposefully infected with a pathogen in order to test the effectiveness of a therapeutic or preventative measure (like a vaccine)?</p>
<p>If not, would the FDA allow for ethical exceptions in cases where there is an extreme case of urgency (like in a pandemic)?</p>
<p>Obviously these would be willing volunteers who signed waivers, etc. So Nazi experimentation, the Tuskegee trial, and other studies without total consent from the participants wouldn't qualify here.</p>
<p>Edit: Self-experimentation wouldn't qualify here either because the bioethics of self-experimentation are different than testing on others. </p>
| [
{
"answer_id": 92362,
"pm_score": 6,
"text": "<p>This is a great biological question! It asks a lot about how empirical science is done in the field of modern biology. I'm glad we encourage such questions from curious people who want to learn more.</p>\n<hr />\n<p>One can't easily separate ethics from h... | [
{
"answer_id": 92375,
"pm_score": 4,
"text": "<p>Yes, Dr Barry Marshall self administered <em>Helicobacter pylori</em> to investigate whether it causes stomach ulcers. He won a Nobel Prize for it.</p>\n\n<p><a href=\"https://en.wikipedia.org/wiki/Barry_Marshall\" rel=\"noreferrer\">https://en.wikipedia.... |
94,172 | <p>There are countless sources, both peer-reviewed and popular, explaining how overuse and misuse of antibiotics is breeding a new generation of antibiotic-resistant "superbugs" such as MRSA (Methicillin-resistant Staphylococcus aureus) and MDR-TB (multidrug-resistant Tuberculosis). Over in the animal kingdom, the opposite seems to be happening - species after species is becoming endangered and/or extinct as humans destroy or alter their habitat through increased hunting, farming, construction, etc.</p>
<p>Are there any non-human <em>animals</em> that have been found to have evolved resistance to human encroachment into or alteration of their habitat in a way analogous to how bacteria have evolved resistance to human attempts to get rid of them? For example, this could consist of:</p>
<ul>
<li>an animal that has adapted stronger bones to better survive collisions with vehicles</li>
<li>an animal that has significantly increased its blood coagulation rate to survive gunshot wounds from hunters</li>
<li>an animal that has developed better vision to see in urban environments</li>
<li>an animal that has evolved a skin pigment change that enables them to not take as much damage when they are sprayed with agricultural pesticides</li>
</ul>
<p>One answer that came to mind is domestic animals - the horse and dog in prehistory, the cat in ancient Egypt, etc. That seems too obvious on one hand, and on the other hand may not really be an answer, as there seems to be no indication that pre-domestic animals were <em>endangered</em> by humans in any meaningful way. Are there animals that have significantly adapted themselves to surviving <em>as wild animals</em> in human-influenced environments?</p>
| [
{
"answer_id": 94174,
"pm_score": 6,
"text": "<p>Note: This is an answer to the last line of your question.</p>\n<p>A classical example of animals adapting to the influence of humans on their environment is the adaption of the <a href=\"https://en.wikipedia.org/wiki/Peppered_moth_evolution\" rel=\"noref... | [
{
"answer_id": 94180,
"pm_score": 5,
"text": "<p>Many insects (as well as some other animals) have documented <a href=\"https://en.wikipedia.org/wiki/Pesticide_resistance\" rel=\"noreferrer\">resistance to pesticides</a>.</p>\n\n<p>For example, the <a href=\"https://en.wikipedia.org/wiki/German_cockroac... |
98,252 | <p>Today I read a <a href="https://www.bbc.com/news/world-latin-america-56011594" rel="noreferrer">BBC Report</a> about how Pablo Escobar had once imported 4 hippos (1 male, 3 female) into his estate in Colombia for his private zoo. After his downfall, while other species were shipped out, hippos were considered too big to move and expected to not survive.</p>
<p>However, to the surprise of all the hippos are thriving and are so numerous that there have been calls to cull them. From the report:</p>
<blockquote>
<p>Numbers are projected to only get bigger. [Colombian biologist Nataly] Castelblanco and her
peers say the population will reach over 1,400 specimens as early as
2034 without a cull - all of them descended from the original group of
a male and three females. In the study, they envisaged an ideal
scenario in which 30 animals need to be culled or castrated every year
to stop that happening.</p>
</blockquote>
<p>My understanding is that since there was only 1 male, the gene pool would be limited and lead to lot of inbreeding in the descendants. This would cause population to not explode because some individuals would be unfit to survive.</p>
<p>Why has this not happened in case of hippos? Is it because there are 3 females (probably unrelated to each other) which keeps gene pool large enough? Or can mutations explain this phenomenon? Would results have been different if originally 2 females had been moved and only 1 retained?</p>
<p><strong>EDIT</strong> - I have just found that <a href="https://en.wikipedia.org/wiki/Pablo_Escobar%27s_hippos" rel="noreferrer">current population</a> is maybe less than 100 individuals which though big is not <em>massive</em>.</p>
<p><strong>EDIT2</strong> - I have edited the question title to keep focus on the hippos although a general answer would be welcome.</p>
| [
{
"answer_id": 98268,
"pm_score": 6,
"text": "<p>I think one of the important things to understand in thinking about this case is that it just hasn't been that long, generationally.</p>\n<p>Escobar imported the hippos <a href=\"https://en.wikipedia.org/wiki/Hippopotamus#Invasive_potential\" rel=\"norefe... | [
{
"answer_id": 98253,
"pm_score": 3,
"text": "<p>They often do. You hear a lot about all of the times invasive species succeed in invading a new habitat, because there is a surviving population around for researchers to observe. There are lots of cases where new species are introduced to an environment ... |
101,641 | <p>I take a great interest in the intersection between science and religion and evolution is therefore something I often read about. Many of the critics of evolution like to poke "scientific" holes in evolution, perhaps the most common one being that there is simply "not enough" evidence. As someone trained in physics but not biology, I would like a book that is accessible and which summarises the evidence we have accumulated for the evolution of life on Earth. Ideally, I would like a book that remains strictly scientific, without any particular atheistic or religious agenda, and which <em>evaluates</em> each line of evidence rather than simply describing it.</p>
<p>Does anyone have a book recommendation?</p>
| [
{
"answer_id": 101646,
"pm_score": 4,
"text": "<p>I like "The Darwinian Revolution" by Michael Ruse.</p>\n<p>It's far more of a history book than a science book. It won't get into the nitty gritty of evidence from molecular biology and modern genetic analyses. What it does do is to chart out h... | [
{
"answer_id": 101643,
"pm_score": 2,
"text": "<p>I think libraries have been filled on the topic of evolution - it is an immensely broad field of study and can be looked at from a geological time scale (millions of years) to a much smaller scale observable in a scientist's career, since evolution drive... |
103,027 | <p>Given that each trophic level of the food chain has a decrease of 90% of available energy, would it be fair to say that 1kg of lettuce has more energy than 1kg of beef? If it's not true, can you explain the reason?</p>
| [
{
"answer_id": 103035,
"pm_score": 7,
"text": "<p>1kg of beef has more energy than 1kg of lettuce but it isn't directly related to the trophic level energy loss.</p>\n<blockquote>\n<p>Given that each level of the food chain has a decrease of 10% of available energy</p>\n</blockquote>\n<p>You're all mixe... | [
{
"answer_id": 103030,
"pm_score": 3,
"text": "<p>The (food) energy in 1kg of lettuce or 1kg of beef depends on each's composition, not on its trophic level. Normally we can digest fats, protein and carbohydrates, but other organisms like certain bacteria and fungi can even digest components like fiber ... |
105,552 | <p>I was watching Vox’s video, <a href="https://www.youtube.com/watch?v=qXdjt8ZBQbE" rel="noreferrer">Big questions about the Covid booster shot, answered</a>, which references the New York Times article <a href="https://www.nytimes.com/2021/12/01/health/covid-omicron-booster-shots.html" rel="noreferrer">Omicron Prompts Swift Reconsideration of Boosters Among Scientists</a>.</p>
<p>In these sources, it is mentioned that the scientific community used to be mostly against giving a booster shot to the less vulnerable. With the emergence of the Omicron variant, the same scientists who were opposed to booster shots have now changed their minds.</p>
<p>However, no complete explanation was given for this, and my further research led to nothing concrete.</p>
<p>As per my understanding, vaccinations provide protection both by increasing antibodies in the blood (which provides protection for about 2 weeks), or by increasing B cells which would be able to identify the spike protein of the virus and help create antibodies (which provides more long-term protection).</p>
<p><strong>With the Omicron variant, my understanding is that there are several mutations in the spike protein, which means that B cells may not recognize it or the antibodies might not bind to its receptors. If this is the concern, then how is the Omicron variant a reason for extra doses of the preexisting vaccines?</strong></p>
| [
{
"answer_id": 105556,
"pm_score": 6,
"text": "<p><em>(note: I'm simplifying things a bit here by only talking about antibodies; I don't mean to downplay other aspects of the immune response, just to keep it focused for a lay audience)</em></p>\n<p>Natural antibody responses by the immune system are <a ... | [
{
"answer_id": 105553,
"pm_score": 2,
"text": "<p>Pathogens (and unfortunately sometimes unrelated things) have antigenic sites. These antigenic sites are responsible for acting as antigens by which an antibody can respond to, or perhaps a larger immune response can initiate. Viruses and pathogens are c... |
111,543 | <p>I was a molecular biology major a while ago, but I never think I really understood cladistics TBH. Now reading about <a href="https://en.wikipedia.org/wiki/Paraphyly" rel="nofollow noreferrer">paraphyly</a>, it shows this:</p>
<p><a href="https://i.stack.imgur.com/ADPsn.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ADPsn.png" alt="enter image description here" /></a></p>
<p><a href="https://i.stack.imgur.com/Tebw7.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Tebw7.png" alt="enter image description here" /></a></p>
<blockquote>
<p>In this phylogenetic tree [second image], the green group is paraphyletic; it is composed of a common ancestor (the lowest green vertical stem) and some of its descendants, but it excludes the blue group (a monophyletic group) which diverged from the green group.</p>
</blockquote>
<p>Looking at the "simiiformes", I can understand why you would call that "monophyly", because everything is connected to a common ancestor. But why not just make the blue area a full blue triangle to make the prosimii and simiiformes one triangle/group? In the end, we all share the same ancestor, so I don't see why they are disconnected.</p>
<p>TBH I'm not sure how to read this at all, and am not following the Wiki description. Can you explain how the 3 terms work for a child or layperson with a better concrete example?</p>
<p>We are all composed of atoms, so we are all made of matter. Matter is made of particles, so we are all made of particles. But light is a particle and we are not made of light, even though in some way "we share the same common ancestor" of the quantum field. But light is still called a particle, so the triangle is the group of all particles. I'm not sure I'm getting on the right track.</p>
<blockquote>
<p>A paraphyletic group is a monophyletic group from which one or more subsidiary clades (monophyletic groups) are excluded to form a separate group.</p>
</blockquote>
<p>Why would they do that?</p>
| [
{
"answer_id": 111544,
"pm_score": 6,
"text": "<p>These are terms to describe names we give things that don't really follow phylogeny accurately. Fish, for example - a monophyletic group involving fish would include humans, too, yet there are many cases where it's useful to talk about fish without meani... | [
{
"answer_id": 111549,
"pm_score": 4,
"text": "<p>One very simple example that most people are familiar with is the <strong>vernacular use of "animal"</strong>. Most people recognize that humans are animals and more closely related to other animals than plants. However, usually when people say... |
6 | <p>I'm interested in sequencing and analyzing the bound DNA, and minimizing the amount of unbound DNA that gets sequenced through digestion.</p>
<p>When digesting protein-bound DNA, is <em>all</em> of the unbound DNA digested? Is there a way to maximize the amount of unbound DNA that is digested?</p>
| [
{
"answer_id": 51,
"pm_score": 3,
"text": "<p>Well, it depends if you just want to sequence your protein bound fragments.\nIf that is the case, I suppose you could go for a FAIRE-seq.\nBasically, you perform several iterative phenol/chlo extractions, thus separating the bound and unbound fragments.\nThe... | [
{
"answer_id": 1184,
"pm_score": 1,
"text": "<p>This is a difficult experiment. It's usually done by digesting the DNA under conditions where the binding protein is solidly attached. DNAse is added, and then after some time, the DNAse is degraded with heat or the addition of an inhibitor. </p>\n\n<p>... |
11 | <p>According to the endosymbiont theory, mitochondria and chloroplasts originated as bacteria which were engulfed by larger cells. How many times is it estimated that this occurred in the past? Are there any examples of this process being observed directly?</p>
| [
{
"answer_id": 60,
"pm_score": 5,
"text": "<p>Well, it seems quite obvious that it was not a single I-eat-you-but-you-survived act but rather a convergence of endosymbiotic and host species into a greater and greater cooperation. \nOf course this leaves a question if there was one or more species of end... | [
{
"answer_id": 116,
"pm_score": 3,
"text": "<p>It depends of what you call endosymbiosis. In the sense of mutualistic interaction between host cell and intracellular organism, it also include Rhizobium bacteria and Fabaceae plants, some Cnidaria and algea in their cells, and even some micorrhizal fungi ... |
32 | <p>What do the strain designations for flu mean?<br>
For example avian flu is classified as <code>H5N1</code>, what do the letters <code>H</code>, <code>N</code> and numbers <code>5</code>, <code>1</code> mean? Is it more than a simple string-identifier?</p>
| [
{
"answer_id": 34,
"pm_score": 6,
"text": "<p>The sub-type is named for the broad classes of the hemagglutinin (HA) or neuraminidase (NA) surface proteins sticking through the viral envelope. There are 16 HA sub-types (designated H1 - H16) and 9 NA sub-types (designated N1 - N9). All of the possible com... | [
{
"answer_id": 35,
"pm_score": 3,
"text": "<p>The two letters represent the type of hemagglutinin (H) and neuraminidase (N) present on the viral surface. Those are the major surface proteins of the influenza virus and therefore crucial for the immune response.</p>\n\n<p>From <a href=\"http://www.ncbi.nl... |
94 | <p>Cerebrospinal fluid (CSF) is produced in the choroid plexus of the lateral ventricles and in the 4th ventricle of the brain. CSF then circulates through the ventricles of the brain and the subarachnoid space of the meninges. CSF is returned to the venous system via the arachnoid granulations connecting the subrachnoid space with the superior sagittal sinus at the superior portion of the neurocranium.</p>
<ul>
<li><p>What circulates the CSF such that it can return to the venous system against gravity? </p></li>
<li><p>In other words, why does CSF not all just pool in the caudal cistern?</p></li>
</ul>
| [
{
"answer_id": 98,
"pm_score": 5,
"text": "<p>There are several points here.</p>\n\n<p><strong>Arachnoid granulations are not the only \"sinks\" for CSF.</strong></p>\n\n<p>Even though it is true that most of the CSF is eliminated from ventricular system and subarachnoid space through these granulations... | [
{
"answer_id": 34197,
"pm_score": 1,
"text": "<p>Circulation of cerebrospinal fluid (CSF) through the ventricular system is driven by motile cilia on ependymal cells of the brain.</p>\n\n<p>Hagenlocher C1, Walentek P, M Ller C, Thumberger T, Feistel K.Ciliogenesis and cerebrospinal fluid flow in the dev... |
166 | <p>Some proteins express well in a heterologous host; others- don't. A few requirements are known to determine the protein expression, like a strong promoter (like T7) for transcription and a strong ribosome binding site for translation. I am working with a protein, which consists of 2 subunits - alpha and beta. Both of them are on a plasmid with T7 promoter in front of the beta subunit (i.e. the construct is T7 promoter, CDS for beta subunit, CDS for the alpha subunit). The beta subunit expresses well, but the alpha doesn't. Do you thing this has something to do with the local environment (promoters, RBSs, etc) and how much does it depend on that? How can I increase the protein expression?</p>
| [
{
"answer_id": 521,
"pm_score": 3,
"text": "<p>I found a very nice paper: <a href=\"http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0CFoQFjAF&url=http://mpec.ucsf.edu/pdfs_new/Pubs_77.pdf&ei=xkMHT-XmKqbdiAKv4JSHCQ&usg=AFQjCNFcrXypViPECyKyeUvRM2JmZti... | [
{
"answer_id": 170,
"pm_score": 3,
"text": "<p>One important aspect when expressing a protein from a different organism in E. coli is that the codon usage of the original organism is likely different from the codon usage of the E. coli used for expression (<a href=\"http://en.wikipedia.org/wiki/Codon_us... |
222 | <p>Many plants (e.g. roses, palms) can be protected from frost during the winter if shielded with an appropriate coat that can be bought in garden shops. Do plants produce any heat that can be kept inside with these "clothes"?</p>
| [
{
"answer_id": 273,
"pm_score": 6,
"text": "<p>Cellular respiration in plants is slightly different than in other eukaryotes because the electron transport chain contains an additional enzyme called <a href=\"http://en.wikipedia.org/wiki/Alternative_oxidase\" rel=\"noreferrer\">Alternative Oxidase</a> (... | [
{
"answer_id": 223,
"pm_score": 4,
"text": "<p>Plants will be respiring continuously, which is an exothermic process. Therefore the plants will be producing a small amount of heat. The protection from frost may be more a result of the vastly smaller convection current of the coat compared to the atmosph... |
228 | <p>What statistical processes and methods are used by geneticists/molecular biologists to know where one gene starts and one ends?</p>
| [
{
"answer_id": 231,
"pm_score": 5,
"text": "<p>I know of only one naive approach to determining the boundaries of a gene : RACE-PCR. There are two kinds, 3' and 5' RACE, which allow to find the respective extremities.</p>\n\n<p>The rationale is the following :</p>\n\n<ul>\n<li><p>You perform a reverse t... | [
{
"answer_id": 229,
"pm_score": 2,
"text": "<p>Generally speaking you sequence the genome and then search for clues. There are usually specific sequences preceding a gene that help the translational equipment know \"hello this is where we begin\" as well as regions where proteins can bind that are used ... |
287 | <p>The chemical difference between RNA and DNA is the missing 2'-hydroxyl group in the nucleotides that build DNA. The major effect of that change that I know of is the higher stability of DNA compared to RNA. But I'm wondering whether this difference has significant implications for the ability of DNA to form compex, three-dimensional structures.</p>
<p>RNA is known to be able to from complex tertiary structures and function as ribozymes. It clearly has the ability to form a wide range of structures and can catalyze a variety of chemical reactions.</p>
<p>As far as I know, there are no naturally occuring catalytic DNAs known. But a number of synthetic DNA enzymes have been created in the lab, so it is generally possible for DNA to form catalytic structures (see <a href="http://dx.doi.org/10.1016/1074-5521%2894%2990014-0">Breaker and Joyce 1994</a> for the first created DNA enzyme).</p>
<p>I'm wondering whether the missing 2'-OH means that DNA has less potential to form complex structures compared to RNA? I imagine it changes the ability to create hydrogen bonds, but I don't know if it would significantly decrease the potential structures that DNA could adopt.</p>
<hr>
<p><sub><a href="http://dx.doi.org/10.1016/1074-5521%2894%2990014-0">Breaker RR, Joyce GF; (December 1994). "A DNA enzyme that cleaves RNA". Chem Biol. 1 (4): 223–9</a></sub></p>
| [
{
"answer_id": 411,
"pm_score": 5,
"text": "<p>To make sure I'm not comparing apples and pears, my (attempt to) answer the question will be broken into two parts: comparison of single-stranded nucleic acids and double stranded ones.</p>\n\n<h3>Single stranded DNA and RNA</h3>\n\n<p>Both DNA and <a href=... | [
{
"answer_id": 296,
"pm_score": 3,
"text": "<p>This is not my field so I'm risking a wrong/incomplete answer here, but I'd say that the critical difference is the almost complete occurrence of double-stranded DNA that precludes the formation of the tertiary structures in single-stranded RNA, rather than... |
306 | <p>I was wondering how many human proteins have a solved 3D structure. Is there a database with only human proteins? I looked at pdb but couldn't find a filter. </p>
| [
{
"answer_id": 309,
"pm_score": 5,
"text": "<p>6405 proteins mapping to 5220 genes, according to Ensembl. </p>\n\n<p>In Ensembl's <a href=\"http://www.ensembl.org/biomart/martview\">BioMart</a>, you can select the PDB ID as external reference. Export the results and count the unique proteins/genes that ... | [
{
"answer_id": 307,
"pm_score": 2,
"text": "<p>From your comments it doesn't seem like you are adverse to writing some custom scripts so one option would be to take advantage of the NCBI Structure database. You can filter it by <a href=\"http://www.ncbi.nlm.nih.gov/structure/?term=human%5BOrganism%5D\"... |
457 | <p>I watched the documentary "Evolve" recently and in the segment on "size" Scott V. Edwards, Harvard evolutionary biologist mentioned the idea that humans might evolve to be 7' tall in 'hundreds of years'. (I think this may have been taken out of context... I have emailed him to find out, but do not expect a response from someone so busy)</p>
<p>The reasoning goes that the trend in the past 100 years has been greater height, and women show a strong preference for men who are taller than they are. (Though a large share perhaps all of this difference has been due to diets higher in protein at an early age) </p>
<p>I wonder, though, if this is only part of the story. The preference women have is not just for tall men, but for a man who is taller than she is. Likewise, men seem to prefer woman who are shorter than they are. There is even cultural pressure: the classic western image of a couple on wedding cake always shows a man who is about 4" (to scale) taller than the bride.</p>
<p>Thus, women who are short have an advantage as they have a greater pool of men to choose from. (Colloquially, simply ask any 6' tall woman if she feels her height helps her find dates.) </p>
<p>Let's say that men seek women who are shorter than they are, but no more than 8" shorter. Women seek men who are taller than they are but no more than 8" taller. Given that the current average height for men is 5'8" and for women it is 5'4" (and distributed normally SD 2.8") will we have selective pressure that leads to greater or lesser height? (This is, obviously, oversimplified, but it is a starting point.)</p>
| [
{
"answer_id": 472,
"pm_score": 5,
"text": "<p>@kate has what is probably the more correct answer for the observed pattern. </p>\n\n<p>But as an experiment, I set up a basic simulation to approximate the conditions that you lay out:</p>\n\n<ol>\n<li>Starting mean heights of 5'8\" (172.72 cm) and 5'4\" (... | [
{
"answer_id": 466,
"pm_score": 4,
"text": "<p><em>(This should have been a comment, but I don't have enough reputation yet. Sorry!)</em></p>\n\n<p>You asked an interesting question, but I'm not sure about your reasoning.</p>\n\n<p>Firstly, the \"trend\" you describe, that in the past century humans gre... |
477 | <p>DNA replication goes in the 5' to 3' direction because DNA polymerase acts on the 3'-OH of the existing strand for adding free nucleotides. Is there any biochemical reason why all organisms evolved to go from 5' to 3'? </p>
<p>Are there any energetic/resource advantages to using 5' to 3'? Is using the 3'-OH of the existing strand to attach the phosphate of the free nucleotide more energetically favorable than using the 3'-OH of the free nucleotide to attach the phosphate of the existing strand? Does it take more resources to create a 3' to 5' polymerase?</p>
| [
{
"answer_id": 478,
"pm_score": 6,
"text": "<p>Prof. <a href=\"http://en.wikipedia.org/wiki/User%3aAgathman\">Allen Gathman</a> has a great 10-minutes <a href=\"http://www.youtube.com/watch?v=y4hKibS2fAo\">video</a> on Youtube, explaining the reaction of adding nucleotide in the 5' to 3' direction, and ... | [
{
"answer_id": 482,
"pm_score": 4,
"text": "<p>DNA replications needs a source of energy to proceed, this energy is gained by cleaving the 5'-triphosphate of the nucleotide that is added to the existing DNA chain. Any alternative polymerase mechanism needs to account for the source of the energy require... |
510 | <p>The accepted range for the wavelengths of light that the human eye can detect is roughly between 400nm and 700nm. Is it a co-incidence that these wavelengths are identical to those in the <a href="http://en.wikipedia.org/wiki/Photosynthetically_active_radiation">Photosynthetically Active Radiation</a> (PAR) range (the wavelength of light used for normal photosynthesis)?</p>
<p>Alternatively is there something <em>special</em> about photons with those energy levels that is leading to stabilising selection in multiple species as diverse as humans and plants? </p>
| [
{
"answer_id": 516,
"pm_score": 8,
"text": "<p>Good question. </p>\n\n<p>If you look at the spectral energy distribution in the accepted answer <a href=\"https://biology.stackexchange.com/questions/450\">here</a>, we see that photons with wavelengths less than ~300 nm are absorbed by species such as ozo... | [
{
"answer_id": 1003,
"pm_score": 4,
"text": "<p>The selection you refer in multiple species could be due to a mutual advantage.\nIf fruits absorb visible wavelengths, they can be spotted by other animals and eaten together with the seeds. Seeds can then mature inside the host and, once eliminated with t... |
532 | <p>I understand bacteria have become resistant to antibiotics due to selection pressures, but how do resistant bacteria process antibiotics when exposed to it, compared to non-resistant bacteria. Also, what research is being conducted to combat bacteria resistant to antibiotics?</p>
| [
{
"answer_id": 533,
"pm_score": 5,
"text": "<p>Bacteria usually gain resistance mechanisms through horizontal gene transfer (such as conjugation and phage infection). The four main mechanisms in which bacteria elude antibiotics are:</p>\n\n<ol>\n<li><strong>Drug Inactivation</strong>: For example, E. co... | [
{
"answer_id": 534,
"pm_score": 4,
"text": "<p>The lead question you have answered yourself: bacteria become resistant because of the selection pressure caused by the antibiotic's effective suppression of the original non-resistant bacteria. Those variants which resist the suppression are selected for ... |
546 | <p>This is a question that has been in my mind since I was a kid. I'm not a doctor, nor even a biology student, just a curious person. What is the minimum and maximum temperature a human body can stand without dying or suffering severe consequences (eg. a burn or a freeze)? While at this subject, how much more global warming will the human body be able to take? Seeing as temperatures keep on rising, I'm just wondering how much longer until the temperature starts having drastic effects.</p>
<p>In my country the temperature is about 35-40-45 degrees Celsius in mid-summer (I live in Romania, eastern Europe, and the climate is supposedly ideal here) which is very unhealthy. Does the human body suffer more and more as the temperatures change?</p>
| [
{
"answer_id": 548,
"pm_score": 6,
"text": "<p><strong>Hypothermia</strong> (when the body is too cold) is said to occur when the core body temperature of an individual has dropped below 35° celsius. Normal core body temperature is 37°C. (<a href=\"http://www.nhs.uk/Conditions/Hypothermia/Pages/Causes.... | [
{
"answer_id": 701,
"pm_score": 4,
"text": "<p>As Rory explained, internal body temperature needs to be highly regulated.</p>\n\n<p>Sweating is the main built in mechanism for removing excess heat from the human body. According to my biology book, in (100%) humid conditions humans cannot survive in heat... |
714 | <p>All humans can be grouped into ABO and Rh+/- blood groups (at a minimum). Is there any advantage at all to one group or the other? <a href="http://rajugurusamy.wordpress.com/2007/10/06/why-blood-types-and-any-advantage/">This article</a> hints that there are some pathogens that display a preference to a blood type (for example <a href="http://Schistosomiasis">Schistosomiasis</a> <em>apparently</em> being more common in people with blood group A, although it could be that more people have type A in the areas that the parasite inhabits). Is there any literature out there to support or refute this claim or provide similar examples? </p>
<p>Beyond ABO-Rh, is there any advantage or disadvantage (excluding the obvious difficulties in finding a donor after accident/trauma) in the 30 other blood type suffixes recognised by the International Society of Blood Transfusions (<a href="http://www.isbtweb.org/home/">ISBT</a>)? </p>
<p>I'd imagine not (or at least very minimal) but it would be interesting to find out if anyone knows more. </p>
| [
{
"answer_id": 747,
"pm_score": 6,
"text": "<p>I've been doing a little more digging myself and have found a couple of other advantages:</p>\n\n<p><strong>Risk of Venous-thromboembolism</strong> (<em>deep vein thrombosis/pulmonary embolism <sup><a href=\"http://www.nhs.uk/conditions/thrombosis/Pages/Int... | [
{
"answer_id": 717,
"pm_score": 4,
"text": "<p>The less antigens a woman (or in fact a female of any species close enough to humans for this phenomenon) has, the higher are the risks of triggering an immune reaction during her pregnancy, if the child has those antigens.<br>\nThe <a href=\"http://en.wiki... |
785 | <p>I am well aware of traditional anaerobic respiration (lactic acid or alcohol produced - no Krebs cycle) and traditional aerobic respiration (O<sub>2</sub> is used at the end of the Citric acid cycle).</p>
<p>I am wondering how to classify respiration that uses the Citric acid cycle, but consumes a nitrite/ate or sulfite/ate instead of O<sub>2</sub>. Is that anaerobic or aerobic?</p>
<p><img src="https://i.stack.imgur.com/OqFkj.jpg" alt="NADH and Nitrite"></p>
<p>I could only find this image on Google image search catch but it said it was from <a href="http://lecturer.ukdw.ac.id/dhira/Metabolism/RespAnaer.html" rel="nofollow noreferrer">http://lecturer.ukdw.ac.id/dhira/Metabolism/RespAnaer.html</a></p>
| [
{
"answer_id": 5678,
"pm_score": 4,
"text": "<p>Your question is based on a bit of confusion about electron acceptors that is very common and that drives microbiologists crazy. Energy (as ATP) is generated when electrons are moved from an electron donor to an electron acceptor. In respiration, the elect... | [
{
"answer_id": 786,
"pm_score": 4,
"text": "<p>Anaerobic respiration is a respiration where the final electron acceptor is different than oxygen. The final acceptor can be a less oxidizing than oxygen, like sulfate (SO<sub>4</sub><sup>2-</sup>), nitrate (NO<sup>3-</sup>), or sulfur (S). For example bact... |
855 | <p>According to <a href="http://en.wikipedia.org/wiki/Vaccine">Wikipedia</a>:</p>
<blockquote>
<p>A vaccine typically contains an agent that resembles a disease-causing
microorganism, and is often made from weakened or killed forms of the
microbe, its toxins or one of its surface proteins. The agent
stimulates the body's immune system to recognize the agent as foreign,
destroy it, and "remember" it, so that the immune system can more
easily recognize and destroy any of these microorganisms that it later
encounters.</p>
</blockquote>
<p><strong>Question</strong>: How does the immune system ""remember"" a foreign agent introduced via a vaccine? And how does it learn how to deal with subsequent encounters?</p>
| [
{
"answer_id": 865,
"pm_score": 5,
"text": "<p>Vaccines work by introducing an attenuated strain of the pathogen (or alternatively the antigens that are normally present on the pathogens surface) into the body, whereupon the body mounts an immune response. As this will (hopefully) be the first time tha... | [
{
"answer_id": 856,
"pm_score": 3,
"text": "<p>In short, some of the B-cells (antibody producing lymphocytes) specified to deal with this agent go dormant after the vaccine stimulation -- when the real danger comes, they can proliferate quickly and flood it with new antibodies, also alerting the rest of... |
935 | <p><a href="http://en.wikipedia.org/wiki/Polyploid">Polyploidy</a> is the multiplication of number of chromosomal sets from 2n to 3n (triploidy), 4n (tetraploidy) and so on. It is quite common in plants, for example many crops like wheat or Brassica forms. It seems to be rarer in animals but still it is present among some amphibian species like Xenopus.</p>
<p>As I know in mammals polyploidy is lethal (I don't mean tissue - limited polyploidy). I understand that triploidy is harmful due to stronger influence of maternal or paternal epigenetic traits that cause abnormal development of placenta, but why there is no tetraploid mammals?</p>
| [
{
"answer_id": 2552,
"pm_score": 6,
"text": "<p>Great question, and one about which there has historically been a lot of speculation, and there is currently a lot of misinformation. I will first address the two answers given by other users, which are both incorrect but have been historically suggested b... | [
{
"answer_id": 946,
"pm_score": 3,
"text": "<p>Plants have a simpler anatomical structure than mammals (is <em>anatomical</em> the right word, or would <em>physiological</em> be more appropriate?). Mammals on average don't have more genes than plants, so my understanding is that this additional complexi... |
1,025 | <p>I'm reading about the use of x-ray crystallography to determine protein structure. According to my book, data is collected at 30-360 angles (dependent on the symmetry of the protein). An illustration is given with concentric rings labelled with distances - the further out the points are, the higher the resolution.</p>
<p>Is the image a composite (where the angle of the point point from the centre is equivalent to the angle of the reading) or is a separate image taken at each angle? Are there any other reasons why more images would be required?</p>
<p>Thanks.</p>
| [
{
"answer_id": 2283,
"pm_score": 4,
"text": "<p>You cannot solve a structure with a single frame, even with perfect diffraction.</p>\n\n<p>The reason you need images over a large swath of angles is because the diffraction pattern is also in three dimensions, in the so-called \"reciprocal space\". At mi... | [
{
"answer_id": 1030,
"pm_score": 2,
"text": "<p>Not by analysing a single protein. There is work with x-ray lasers. </p>\n\n<p>You have to take a simultaneous image of millions of proteins and use that to get a structure. It's not quite prime time. People are also doing this with electron beams in e... |
1,071 | <p>Do insects with compound eyes have depth perception? They fly as if they do, but their eyes are so close together it seems like the image would be 2 dimensional.</p>
| [
{
"answer_id": 1080,
"pm_score": 4,
"text": "<p>\"1001 questions answered about insects\" by Alexander Barrett and Elsie Broughton Klots includes the following passage:</p>\n\n<blockquote>\n <p><strong>Do insects have depth perception?</strong> Depth perception of some sort is important to an animal wh... | [
{
"answer_id": 1083,
"pm_score": 3,
"text": "<p>The sense of depth is required to us to orient ourselves in a 3D world. Insects do orient themselves in the exterior 3D world, thanks to the ability to detect the plane of sunlight polarization, that is used as a navigation compass in foraging expeditions ... |
1,116 | <p>My cat is about 1' high at the shoulder, and I am a little over 6', but my cat can easily jump onto something as high as I am. That is 6x it's height. If a cat can do this, then Why can't I jump up onto my barn roof? That is a little less than 36' up. I have a hard time jumping onto even a 4' platform. Now if my cat had trouble jumping onto an 8" platform, I would think that pathetic. Do cats have muscles 20x stronger than humans, for their mass?
Is it just their skeleton providing leverage?</p>
| [
{
"answer_id": 7320,
"pm_score": 2,
"text": "<p>Cats have different body structure than human beings. Its body-kinetics are quite different from us. Yes, muscles are quite strong, but this not the only reason. To know in-depth about the reasons behind the cats’ extreme jumping abilities, you can just re... | [
{
"answer_id": 1121,
"pm_score": 3,
"text": "<p>There is not a linear relationship between the size of a muscle and its power. The cat weighs significantly less, but the decline in muscle power is not identical. If he weighs 20x less than you, but his muscle generate 1/5 as much force, he will still be ... |
1,126 | <p>Some genes have been shown to be <a href="http://www.ncbi.nlm.nih.gov/pubmed/17667961" rel="noreferrer">associated with left-handedness</a>.</p>
<p>Working with some clinicians, I've recommend them to ask their patients (whose genome will be sequenced) if they are "right or left-handed".
It's a simple phenotype (without any ethical issue) that will be later fun/interesting to analyze through the sequencing data outside of the main study.</p>
<p>Do you know any other such kind of simple phenotype that we could ask to our patients ? :-)</p>
| [
{
"answer_id": 1128,
"pm_score": 4,
"text": "<p><a href=\"https://www.23andme.com/\">23andMe</a> is a company that provides sequencing. Before they sequence your genome, they ask you to fill in a couple of surveys, one of which is about your physical features. Here is a list of some of the questions the... | [
{
"answer_id": 1141,
"pm_score": 3,
"text": "<p>Another <a href=\"http://bioweb.wku.edu/courses/biol114/genetics/human_genetics/human_genetics1.asp\" rel=\"nofollow noreferrer\">list of simple human traits</a> can be found on the Western Kentucky University site.</p>\n\n<p>I will ask also AB0 and Rh Blo... |
1,133 | <p>I read somewhere (I think it was Bill Bryson's book on the origins of the English language) that of all animals, we are the only ones that can choke on food (having something to do with how our larynx is positioned). I'm unable to find reference to this fact online, however, and am curious if this is just my having misunderstood something (or Bill having led me astray!). </p>
| [
{
"answer_id": 9392,
"pm_score": 5,
"text": "<p>From the Smithsonian website:</p>\n\n<p>Humans are the only mammal that cannot breathe and swallow at the same time, and we are the only species that can choke on its own food. The reason? The lowering of the voice box in our throats (during infancy) enabl... | [
{
"answer_id": 1149,
"pm_score": 4,
"text": "<p>The veterinarian in our group offers this: For humans, who choke much more frequently than other mammals, it is likely to be a cognitive problem. We talk and eat at the same time and so give ample opportunity to allow food passed the epiglottis and choking... |
1,167 | <p>When reading my textbook I noticed that in all examples but one from eight the recognition site was an even number of bases. </p>
<p>I wondered if this was just a co-incidence, so I took the data from <a href="http://www.thelabrat.com/restriction/enzymesA.shtml" rel="nofollow noreferrer">this site</a> for over a thousand known recognition sites and put it into a spreadsheet (<a href="http://www.mediafire.com/?m5i78wp7pgnii22" rel="nofollow noreferrer">XLS uploaded here</a>). The results are probably best summarised graphically:</p>
<p><img src="https://i.stack.imgur.com/EILPS.png" alt="restriction enzymes pie chart"></p>
<p><img src="https://i.stack.imgur.com/reKKN.png" alt="restriction enzymes bar chart"></p>
<p><strong>Stats Test</strong>: Chi Squared Goodness of Fit.</p>
<pre><code>Null Hypothesis:
There is no significant difference between the number of restriction sequences
that are an odd or even length.
|---------|----------|----------|-----|-------|----------|
| Trait | Observed | Expected | O-E |(O-E)^2|(O-E)^2 /E|
|---------|----------|----------|-----|-------|----------|
| Odd | 172 | 231.5 |-59.5|3540.25| 15.293 |
| Even | 291 | 231.5 | 59.5|3540.25| 15.293 |
|---------|----------|----------|-----|-------|----------|
Chi Squared Value = 30.586
P=0.05, 1 Degree of Freedom: Critical Value of 3.841
H0 rejected with 95% confidence (indeed with 99.9%+ confidence)
</code></pre>
<p>Can anyone explain or suggest why it is more common that restriction enzymes recognition sites have an even number of bases? </p>
<h2>Updates</h2>
<ul>
<li>Expanded dataset to include <a href="http://rebase.neb.com/cgi-bin/seqsget?L%20ed" rel="nofollow noreferrer">new recognition sites</a> from the resource that <a href="https://biology.stackexchange.com/users/444/96well">96well</a> linked to. </li>
<li>Removed all duplicate recognition sites leaving 465 distinct recognition sequences (<em>my fault for not removing them in the first instance</em>)</li>
<li>Ran stats test on the data</li>
<li><em><a href="https://biology.stackexchange.com/revisions/1167/1">See Previous Version</a></em></li>
</ul>
| [
{
"answer_id": 1207,
"pm_score": 5,
"text": "<p>I think this is due to the over-representation of recognition sites with length 6:</p>\n\n<pre><code>data<-c(16, 16, 12, 12, 6, 6, 6, 6, 4, 16, 6, 6, 6, 6, 15, 15, 6, 6, 6, 6, 11, 11, 6, 6, 4, 4, 6, 6, 11, 12, 6, 6, 23, 23, 6, 6, 6, 6, 9, 12, 4, 4, 6, 6... | [
{
"answer_id": 1168,
"pm_score": 2,
"text": "<p>Most restriction enzymes recognize palindromes, hence the recognition site of an even number of residues. Why palindromes? This allows for a vast increase in complexity (or rarity) from a DNA sequence standpoint, while requiring very little added complexit... |
1,310 | <p>When are population dynamics models useful? There seems to have been a lot of research about it, but how does it help? If I need data about how a population will evolve under what conditions, I need it because I need data for a decision (such as "can we kill 50% of population X without doing too much damage?"), right? But for that, the model needs to be aware of what causes what. And for that, I have to do experiments, right? Like "let's kill a significant amount of population X and see what happens in the next ten years". I really don't get it.</p>
| [
{
"answer_id": 1312,
"pm_score": 5,
"text": "<p>Population dynamics occupies a whole subset of mathematical biology. Perhaps the most pragmatic uses for modelling population dynamics come from the fields of epidemiology for modelling disease infection and transmission through a population (<a href=\"htt... | [
{
"answer_id": 1323,
"pm_score": 3,
"text": "<p>Leonardo's already given you an excellent answer, but I thought I'd add my perspective. I'm a mathematical epidemiologist, so I'd at least like to believe these types of models are useful.</p>\n\n<p>For me, there are a number of things population dynamics ... |
1,382 | <p>Which animal/plant/anything has smallest length genome? </p>
| [
{
"answer_id": 1392,
"pm_score": 7,
"text": "<p>Since you said plant/animal/anything, I offer the smallest genomes in various categories...</p>\n<p>(Kb means Kilobases, Mb means Megabases. 1 Kb = 1000 base pairs, 1Mb = 1000Kb)</p>\n<ul>\n<li>Smallest plant genome: <em>Genlisea margaretae</em> at 63Mb (<... | [
{
"answer_id": 1385,
"pm_score": 3,
"text": "<p>I want to say <em>Mycoplasma genitalium</em> with a genome size of 582,970 bp. Turns out the answer is <em>Nanoarchaeum eqitans</em> with a genome of 490,885 bp.</p>\n\n<p><a href=\"http://en.wikipedia.org/wiki/Nanoarchaeum\">http://en.wikipedia.org/wiki/N... |
1,521 | <p>Many fungi undergo a reproductive phase in which more than one genetically distinct nuclei (from 2 separate mating types) is present within the same cytoplasm. In the Ascomycota and Basidiomycota, this phase is termed "dikaryotic", whereas in other fungal phyla the phase is "heterokaryotic." What is the difference here? Is it purely number of nuclei per cell, or does the difference depend on how many genetically distinct nuclei are present (2 or >2)? </p>
| [
{
"answer_id": 1687,
"pm_score": 4,
"text": "<p>A heterokaryon is a fungal cell which has <em>two or more genetically-distinct but allelically-compatible nuclei</em>, as suggested by <a href=\"http://crosswords911.com/heterokaryon.jsp?q=aHR0cDovL3d3dy5lYmkuYWMudWsvaW50ZXJwcm8vSUVudHJ5P2FjPUlQUjAxMDgxNg=... | [
{
"answer_id": 39705,
"pm_score": 1,
"text": "<p>dikaryotic does - by definition - mean that there are exactly two nuclei in the cells, it does not say that the two nuclei are genetically distinct!\nheterokaryotic does also mean only one thing: the nuclei (the number is not important) are genetically di... |
1,767 | <p>The dinosaurs, mammoths, giant plants etc are known to be bigger than modern animals. I wonder why they had been lived and why they are not living now? I really don't know much but is it something about oxygen balance or something similar? </p>
| [
{
"answer_id": 1774,
"pm_score": 5,
"text": "<p>Thanks for asking an interesting question which made me think.</p>\n\n<p>The short answer is that something evolves if there is an advantage to the genes involved, and, by 'advantage' I mean it produces more copies of the genes in the next generation so mo... | [
{
"answer_id": 1778,
"pm_score": 3,
"text": "<p>to expand on Rose's answer, certain environmental factors are what people cite with unusual size changes in an animal over time as it diversifies into new species. </p>\n\n<p><a href=\"http://en.wikipedia.org/wiki/Island_gigantism\">Gigantism (and dwarfis... |
1,795 | <p>There seems to be a lot of redundancy in PDB files. These files can of course be compressed with general-purpose compression programs like gzip, but I can't help but imagine that these tools are overlooking a significant amount of redundancy in PDB files. Are there compressors that specifically target PDB files? If not, what are some aspects of PDB files that are ripe for compression?</p>
<p>Looking at a typical PDB file, some redundancies are immediately apparent. Other redundancies are less obvious. Consider this excerpt of two residues from <a href="http://www.rcsb.org/pdb/files/1MBO.pdb" rel="nofollow">1MOB</a> (myoglobin):</p>
<pre><code>ATOM 332 N LYS A 42 16.481 27.122 -10.033 1.00 11.15 N
ATOM 333 CA LYS A 42 15.926 28.134 -9.159 1.00 8.64 C
ATOM 334 C LYS A 42 16.970 29.081 -8.512 1.00 16.74 C
ATOM 335 O LYS A 42 16.687 30.075 -7.799 1.00 11.84 O
ATOM 336 CB LYS A 42 15.093 27.489 -8.043 1.00 18.03 C
ATOM 337 CG LYS A 42 13.731 26.888 -8.502 1.00 19.65 C
ATOM 338 CD LYS A 42 12.679 27.912 -8.953 1.00 17.94 C
ATOM 339 CE LYS A 42 11.438 27.406 -9.703 1.00 24.82 C
ATOM 340 NZ LYS A 42 10.474 28.567 -9.803 1.00 19.81 N
ATOM 341 N PHE A 43 18.218 28.599 -8.544 1.00 12.28 N
ATOM 342 CA PHE A 43 19.311 29.318 -7.919 1.00 11.81 C
ATOM 343 C PHE A 43 20.223 30.024 -8.949 1.00 10.95 C
ATOM 344 O PHE A 43 21.201 29.462 -9.450 1.00 10.08 O
ATOM 345 CB PHE A 43 20.138 28.301 -7.137 1.00 9.30 C
ATOM 346 CG PHE A 43 19.494 27.689 -5.877 1.00 9.53 C
ATOM 347 CD1 PHE A 43 19.572 28.376 -4.679 1.00 12.01 C
ATOM 348 CD2 PHE A 43 18.837 26.465 -5.923 1.00 10.54 C
ATOM 349 CE1 PHE A 43 18.993 27.861 -3.536 1.00 9.59 C
ATOM 350 CE2 PHE A 43 18.261 25.959 -4.775 1.00 8.62 C
ATOM 351 CZ PHE A 43 18.341 26.666 -3.597 1.00 7.89 C
</code></pre>
<p>These two residues occupy 1,638 bytes as plain text; when compressed with gzip, they occupy 467 bytes. For reference, the format of ATOM records in PDB files is defined at wwpdb.org/documentation/format33/sect9.html#ATOM.</p>
<p>Almost all of the data in the above excerpt seems redundant. The first field (ATOM), second field (atom index, e.g. 332 in the first row), sixth field (residue index, e.g. 42), tenth field (occupancy, e.g. 1.00) and last field (element name, e.g. N) seem clearly extraneous. The fourth field (residue name) could be shortened from three characters to 1 character, or simply an integer. I'm not a data compression expert, but I imagine gzip picks up most of this redundancy.</p>
<p>Slightly less obviously, the atom names for each residue also seem unnecessary. To my understanding, the atomic composition of all residues' backbones will always be the same, and represented in PDB files as "N", "CA", "C", "O". The same for the atomic composition of the residues' respective sidechains: a lysine sidechain will always be "CB", "CG", "CD", "CE", "NZ" and a phenylalanine sidechain will always be "CB", "CG", "CD1", "CD2", "CE1", "CE2", "CZ". </p>
<p>A subtler redundancy, but one that might increase compressibility a lot, seems like it could be in the atomic coordinates themselves. For example, in the backbone, would it be possible to deduce each residue atom's X, Y and Z coordinates (12 data points: 4 atoms * 3 coordinates) given only their phi, psi and omega <a href="http://en.wikipedia.org/w/index.php?title=Dihedral_angle&oldid=474965018#Dihedral_angles_of_biological_molecules" rel="nofollow">dihedral angles</a> (3 data points)? Could applying dihedral angles to atoms within sidechains similarly remove the need to explicitly list the 3D coordinates there?</p>
<p>Could "temperature factor" (the second to last field in the excerpt) be losslessly removed, or compressed in some non-obvious way? What are some other possible optimizations that could be used to more efficiently compress PDB files? Are there any obvious grave performance implications of these various compression techniques on the speed of a hypothetical decompressor to convert back to the official PDB format? Have these questions been answered in the literature or an existing PDB-specific compression program?</p>
<p>Thanks in advance for any answers or feedback.</p>
<p><strong>Edit</strong>:</p>
<p>Given that no PDB-specific file compressors seem to be available, I suppose my specific goal is to develop one. One potential application I see for this is in significantly decreasing fresh times-to-render in certain use cases of browser-based molecular visualization programs, e.g. <a href="http://jmol.sourceforge.net/" rel="nofollow">Jmol</a>, <a href="http://web.chemdoodle.com/" rel="nofollow">ChemDoodle Web Components</a> or <a href="http://webglmol.sourceforge.jp/glmol/viewer.html" rel="nofollow">GLmol</a>. Another application could be decreasing the time and size of data needed to download archives of PDB files like those described <a href="http://www.wwpdb.org/downloads.html" rel="nofollow">here</a>. </p>
<p>This would of course require a way to efficiently decompress the packed PDB files, but this trade-off between decompression time and download time seems like it could be useful in at least some niche applications.</p>
<p><strong>Edit 2</strong>:</p>
<p>In a comment, nico asks "How would compressing the file decrease render time?". Decreasing gzipped PDB file size (e.g. by half or more) and thus decreasing time needed to download the file would decrease the time between when the PDB file was requested from a remote server and when the structure was rendered by a molecular visualization program running on a client machine. Apologies if that use of "fresh time-to-render" in that context was unclear.</p>
<p>A lossless compression could also involve encoding the PDB file to an object (e.g. JSON) that is faster to parse for the visualization program, and decrease render times that way. Looking around further, if the application only required displaying the 3D structure and not also retaining data about specific atoms and residues, then using a binary mesh compression (e.g. <a href="http://code.google.com/p/webgl-loader/" rel="nofollow">webgl-loader</a>) seems like it would probably decrease time-to-render even more.</p>
| [
{
"answer_id": 1797,
"pm_score": 4,
"text": "<p>You are making a few assumptions that are likely not valid for all PDB files. For example:</p>\n\n<ul>\n<li>Residue indices are not necessarily sequential, nor do they have to start at 1</li>\n<li>Not all possible residues have 1-letter code equivalents, t... | [
{
"answer_id": 1796,
"pm_score": 2,
"text": "<p>The PDB file format was specified in the dawn of computing to fit on punch cards. So it has some shortcomings that have led to generations of scientists cursing the fixed-width column format. By now, it has been superseded by an XML-like format: PDBML. Of ... |
1,869 | <p>I was walking down a road with these beautifully huge trees when this question occurred to me. </p>
<p>Large trees with many thick branches have to grow equally in all directions, or they would tip over. Is there some sort of mechanism to ensure this uniform growth? Or is it just a happy coincidence arising from uniform availability of sunlight on all sides? If one branch of a tree becomes too heavy due to many sub-branches, does this somehow trigger growth on the opposite side of the tree? </p>
<p>I have seen that potted plants in houses tend to grow towards sunlight. My mum often turns pots around by 180 degrees to ensure that plants don't bend in any one direction. I assume that this is because sunlight increases the rate of photosynthesis, leading to rapid growth of the meristem.
For trees growing in open spaces, this wouldn't be a problem. But there are many large trees that grow in the shadow of buildings without bending away from the buildings, even though this is the only direction from which they would receive any sunlight. Is there any explanation for this?</p>
| [
{
"answer_id": 1887,
"pm_score": 5,
"text": "<p>Growth in plants is tightly controlled by <a href=\"http://en.wikipedia.org/wiki/Auxin\" rel=\"nofollow noreferrer\">auxins</a> – plant hormones. Auxin itself usually has an <del>inhibitory</del> effect on growth [EDIT: see comments and Richard’s answer fo... | [
{
"answer_id": 1877,
"pm_score": 4,
"text": "<p>They don't always. For example, this apple tree grows just outside my window:</p>\n\n<p><img src=\"https://i.stack.imgur.com/3kNWU.jpg\" alt=\"Tilted apple tree\"></p>\n\n<p>So far, it hasn't fallen over yet. The reason it grows that way is because all t... |
1,917 | <p>I'm hoping to learn the basics of epidemiological methods, terminology, etc. I come from a background in statistical economics, and I'm moving into the economics of public health. I don't know if epidemiology uses separate statistical methods, but I presume it does. I know discussion questions aren't recommended, but please list any reasons you have (personal experience, ease of introduction, etc.) for texts you would recommend. </p>
| [
{
"answer_id": 1996,
"pm_score": 4,
"text": "<p>There are two books I'd highly recommend for someone starting to dabble in Epidemiology. The first is Kenneth Rothman's <em>Epidemiology: An Introduction</em>, which I'm affectionately going to refer to as \"Baby Rothman\" from hereon out for reasons that ... | [
{
"answer_id": 1926,
"pm_score": 3,
"text": "<p>Here is an online book of epidemiology for the uninitiated. I used it to get a basic understanding of epidemiology.</p>\n\n<p><a href=\"http://www.bmj.com/about-bmj/resources-readers/publications/epidemiology-uninitiated\">http://www.bmj.com/about-bmj/reso... |
1,970 | <p>When food is scarce, the body slows its metabolic rate to conserve energy. Are there any other systems or processes that prioritize which organs receive nutrients?</p>
| [
{
"answer_id": 44250,
"pm_score": 3,
"text": "<p>Glucose is prioritized for the brain and erythrocytes over the muscle and adipose tissue, for example, by hormonal control.</p>\n<p>The hormones insulin and glucagon respond to strarvation, insulin secretion falling and that of glucagon increasing. The gl... | [
{
"answer_id": 1974,
"pm_score": 3,
"text": "<p>The glycogen in the liver begins providing blood glucose. Muscle glycogen is used as fuel by the muscles, fat cells (adipose tissue) release fatty acids to manufacture ketone bodies in the liver and to be used by the brain as fuel, and body proteins are co... |
1,981 | <p>Somewhere I have read we share more than 99% of our genes with every other other person and 98% of our genes with chimpanzees. What does this mean? Don't we share 50% of our genes with our mother and 50% with our father?</p>
<p>I've found an another <a href="http://www.scientificamerican.com/article.cfm?id=what-does-the-fact-that-w">article</a> stating that.</p>
| [
{
"answer_id": 1984,
"pm_score": 6,
"text": "<p>There is a distinct difference between the 'genes' that we share, and the genome (the DNA) that the genes are made of.</p>\n\n<p>All humans (excluding genetic disorders) have the same genes, but the same gene in different individuals may have a slightly di... | [
{
"answer_id": 1983,
"pm_score": 4,
"text": "<p>In every cell of your body, you have <strong>two physical copies</strong> of every gene (ignoring gametes, / copy number variations), one from your mother, one from your father. (Humans are <a href=\"http://en.wikipedia.org/wiki/Diploid#Diploid\">diploid</... |
2,051 | <p>I was wondering what exactly a coupled reaction is and why cells couple them. I read the wikipedia article as well as several others, such as <a href="http://www.life.illinois.edu/crofts/bioph354/coupled.html">life.illinois.edu</a> but I still don't get it. Could someone explain it to me?</p>
| [
{
"answer_id": 2052,
"pm_score": 5,
"text": "<p>It's pretty simple. A reaction occurs that releases energy (like ATP losing a phosphate to become ADP + Pi). If this is uncoupled, the energy will merely turn into heat. If it is coupled, then it can be used to fuel some other process. For instance, if you... | [
{
"answer_id": 2903,
"pm_score": 5,
"text": "<p>A reaction where the the free energy of a thermodynamically favorable transformation, such as the hydrolysis of ATP, and a thermodynamically unfavorable one, are mechanistically joined <em>into a new reaction</em> (or may be envisaged to be so joined) is ... |
2,073 | <p>I'd be tempted to call nipples in men vestigial, but that suggests they have no modern function. They <em>do</em> have a function, of course, but only in women. So why do <em>men</em> (and all male mammals) have them? </p>
| [
{
"answer_id": 39769,
"pm_score": 6,
"text": "<p>The two key concepts here are: </p>\n\n<ol>\n<li><strong>sex-specific selection</strong>, and the fact that </li>\n<li><strong>males and females share the majority of genes</strong></li>\n</ol>\n\n<p><strong>1) sex-specific selection</strong></p>\n\n<p>Ob... | [
{
"answer_id": 2102,
"pm_score": 5,
"text": "<p>I believe it is for this reason: the female body plan is the default one. Males are a variation upon that, in humans at least. Nipples are part of the basic body plan. For a man to <em>not</em> have them, he would need to actively evolve something that wou... |
2,076 | <p>We can encode sound and images in radio waves and send them, but presumably there's some physiological reason that we can't easily make a picture or video of a smell. Could we realistically break smells down into "primary scents", in analogy with "primary colors" and encode the information for easy reproduction? </p>
| [
{
"answer_id": 2078,
"pm_score": 5,
"text": "<p>There are only <a href=\"http://en.wikipedia.org/wiki/Cone_cell\">three kinds</a> of optical receptors in the eye, but more than <a href=\"http://en.wikipedia.org/wiki/Olfactory_receptor\">900 kinds</a> of olfactory receptors. Thus you can encode pictures ... | [
{
"answer_id": 2086,
"pm_score": 3,
"text": "<p>In expansion to biocs' excellent answer, I would like to highlight some practical limitations of this. Suppose we <em>did</em> manage to create a huge database of exact chemical mixtures which produce all smells recognisable by humans. You would still meet... |
2,250 | <p>One of my friends said that I would die if I drank distilled water (we were using it in a chemistry experiment) I gave it a go and surprisingly did not die.</p>
<p>I did a bit of <a href="https://www.google.com/search?ie=UTF-8&oe=utf-8&q=drinking+disti%3Blled+water+harmful%3F#hl=en&sa=X&ei=PLyvT9PvPMSIrAesu8mJBA&ved=0CB4QvwUoAQ&q=drinking+distilled+water+harmful%3F&spell=1&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.,cf.osb&fp=311369616e4b455a&biw=1280&bih=652">Googling</a> and found <a href="http://answers.yahoo.com/question/index?qid=20060919161158AAWqN9V">this</a> </p>
<p>It said that drinking only this kind of water could definitely cause death, as distilled water was highly hypotonic and it would make the blood cells expand and finally explode and ultimately cause death.</p>
<p>I wanted to know exactly how much of this water on an average was needed to be consumed to cause death. </p>
| [
{
"answer_id": 7194,
"pm_score": 7,
"text": "<p>I'm extremely skeptical of @leonardo's answer. I suspect that what would happen if you drank only distilled water is nothing perceptible. The only place where concentrations of distilled water would ever be high enough to conceivably matter is in the tis... | [
{
"answer_id": 2253,
"pm_score": 6,
"text": "<p>Drinking a <em><strong>little bit</strong></em> of distilled water is not fatal. Drinking <em><strong>only</strong></em> this kind of water and ingesting nothing else will eventually be fatal because it is highly hypotonic as you've found out.</p>\n\n<p>Sa... |
2,348 | <p>I always wondered why gametes from two different species dont fuse together to form an offspring. eg a donkey (sperm) and a female dog (egg) </p>
<p>I know this is not possible but I'm just curious. </p>
| [
{
"answer_id": 2358,
"pm_score": 4,
"text": "<p>Daniel's answer excellently explains the issue in an understandable fashion, though you may have been looking for a more cell biological approach.</p>\n\n<p>According to <a href=\"http://www.ncbi.nlm.nih.gov/pubmed?term=sperm%20cannot%20penetrate%20egg%20o... | [
{
"answer_id": 2355,
"pm_score": 3,
"text": "<p>The biological environment in every cell and tissue of your body is an extremely complex, tightly controlled system. There are tens of thousands of genes in a typical eukaryotic genome, and depending on tissue types and environmental conditions, these gene... |
2,507 | <p>What are they, and do they share a common ancestor? How far back in evolutionary time must we go to find them?</p>
<p>If none are known, what computational tools might be used to search for such examples?</p>
| [
{
"answer_id": 2520,
"pm_score": 4,
"text": "<p>The answer is that common folds are discovered in sequences which are completely divergent where essentially no alignment can be found by conventional means. </p>\n\n<p>David Eisenberg's group created profiles based on alignments from known structures whi... | [
{
"answer_id": 2510,
"pm_score": 3,
"text": "<p>This <a href=\"http://dx.doi.org/10.1109/TCBB.2009.28\" rel=\"nofollow\">paper</a> published last year, address the answer for your question, about computational methods, they mention 3 principal algorithms for structural alignment\nof proteins:</p>\n\n<ul... |
2,738 | <p>Why, from the natural selection point of view, do only two sexes exist for animals?</p>
| [
{
"answer_id": 2796,
"pm_score": 6,
"text": "<p>To get a non-circular answer to why humans and other mammals have only two sexes, it's helpful to take a look at our evolutionary history. While mammals possess several adaptations to a terrestrial life cycle, including internal fertilization and gestatio... | [
{
"answer_id": 2745,
"pm_score": 3,
"text": "<p>@emanuele you seem to be asking why there are only 2 sexes for animals, in contrast to f<a href=\"http://blog.mycology.cornell.edu/?p=1060\" rel=\"nofollow\">ungi which can have many sexes</a> or maybe bacteria which have mobile sex - the ability to donate... |
2,739 | <p>Shortly before his untimely passing, the computing pioneer Alan Turing published his most cited paper <a href="http://www.cecm.usp.br/~cewinter/aulas/artigos/2010/Turing_1952.pdf"><em>The Chemical Basis of Morphogenesis</em></a> (1952). </p>
<p>The central question for Turing was: how does a spherically symmetric embryo develop into a non-spherically symmetric organism under the action of symmetry-preserving chemical diffusion of <em>morphogens</em> (as Turing calls them, an abstract term for arbitrary molecules relevant to development)? The insight that Turing made is that very small stochastic fluctuations in the chemical distribution can be amplified by diffusion to produce stable (i.e. not time varying except slow increases in intensity; although also potentially time-varying with 3 or more morphogens) patterns that break the spherical symmetry.</p>
<p>The theory is beautifully simple and abstract, and produces very important qualitative results (and also quantitative results through computer simulation, which unfortunately Turing did not get to fully explore). However, even in the definition Turing discusses some potential limitations such as ignoring mechanical factors, and the inability to explain preferences in handedness. The particular models he considers -- a cycle of discrete cells and a circular tissue -- do not seem particularly relevant. As far as I understand, the key feature is his observation of symmetry breaking through small stochastic noise and instability. </p>
<p><strong>What was the most important contribution of Turing's paper to developmental biology? Is his approach still used, or has the field moved on to other models? If his approach is used, how was the handedness problem resolved?</strong></p>
| [
{
"answer_id": 3352,
"pm_score": 4,
"text": "<p>This is a very interesting question. Many people have researched this topic, and many still are. But regardless, I had never heard of Alan Turing's contributions, so thank you!</p>\n\n<p>First of all, I cannot actually find who first coined the term morpho... | [
{
"answer_id": 3371,
"pm_score": 2,
"text": "<p>I would think this is very much still \"used.\" 60 years later, we finally have the first experimental support for it: </p>\n\n<p>In this <a href=\"http://www.sciencedaily.com/releases/2012/02/120219143321.htm\" rel=\"nofollow\">blog article about</a> this... |
2,835 | <p>I am conducting an investigation into the effect of two different grass management techniques (grazing vs. machine-mowing) upon floral biodiversity.</p>
<p>I have collected my data and now need to process it in a way that will yield meaningful and valid results. My data is in the form of 25 samples per area with %-abundance measured for each species in a 0.25m<sup>2</sup> quadrat.</p>
<p>I am currently using a non-standard diversity quantification technique, called Disney's index (which I have been led to believe is named eponymously after R.H.L Disney, however I am unable to find any references describing this), in which we assign each species a weight based on percentage abundance, as follows:</p>
<p> <img src="https://i.stack.imgur.com/cMdor.png" alt="Table showing weights for %-abundances"></p>
<p>We then use these weights to calculate the index as follows (i.e. by computing the sum of the weights of the species, over the number of species):</p>
<p> <img src="https://i.stack.imgur.com/HXHiB.png" alt="enter image description here"></p>
<p>I want to know if this is the best possible diversity index I could use for this type of analysis, or whether there are others which I should be considering.</p>
<p>Thanks in advance!</p>
| [
{
"answer_id": 2836,
"pm_score": 4,
"text": "<p>It sounds like you are interested in <a href=\"https://en.wikipedia.org/wiki/Beta_diversity\" rel=\"nofollow noreferrer\">beta diversity</a> which is the change in taxa composition (i.e., alpha diversity) between plots. There are a number of approaches to... | [
{
"answer_id": 3059,
"pm_score": 2,
"text": "<p>I don't know anything about the \"Disney index\" but the equation you use looks like it's a version of Simpson's D, a very common biodiversity index. If you're just estimating two different kinds of sites (your two management strategies) I would suggest a... |
2,838 | <p>Suppose that we have the ability to make mosquitoes extinct, what would be the likely effects (on disease and ecosystems for example) of such extinction? Essentially, what roles in nature do mosquitoes perform?</p>
| [
{
"answer_id": 2836,
"pm_score": 4,
"text": "<p>It sounds like you are interested in <a href=\"https://en.wikipedia.org/wiki/Beta_diversity\" rel=\"nofollow noreferrer\">beta diversity</a> which is the change in taxa composition (i.e., alpha diversity) between plots. There are a number of approaches to... | [
{
"answer_id": 3059,
"pm_score": 2,
"text": "<p>I don't know anything about the \"Disney index\" but the equation you use looks like it's a version of Simpson's D, a very common biodiversity index. If you're just estimating two different kinds of sites (your two management strategies) I would suggest a... |
2,955 | <p>It may be different for other people, but for me, anything above 32°C (90°F) is very uncomfortable, and my body is inclined to seek cooler temperatures. But I would think that at 32°C, the body would have less work to do to get itself to 37°C. So why is it not comfortable in those temperatures?</p>
<p>My theory is this, but I don't know if it's right: </p>
<p>The body's abilities for warming itself are much more sophisticated than its abilities for cooling itself (which are non-existent, possibly?). So it likes to be in an environment 20-30 degrees below optimal because it can easily handle that. But up in the 32's and we're dangerously close to going over the optimal, and the body doesn't know how to get it back down after that, so we are inclined to seek safer temperatures. </p>
<p>Is it something like that?</p>
| [
{
"answer_id": 2956,
"pm_score": 5,
"text": "<p>The body can never stop working. If the body stops working, you die.\nAnd while the body is working it cannot avoid generating heat.\nBeing in an environment somewhat colder than the body makes getting rid of this excess heat easier, and is thus more comfo... | [
{
"answer_id": 2959,
"pm_score": 3,
"text": "<p>Your body requires energy to function. Just like in a powerplant, the energy comes from oxidizing fuel (food, instead of coal or gas). The efficiency Of conversion is rather low, and results in excess heat, which must be rejected to the environment. Whe... |
3,169 | <p>Other than CO₂ and Methane what other gases do humans produce or emit?</p>
<p>For example, does skin decomposition, or aerobic respiration emit any special gases that people don't normally realize or know about.</p>
<p>I ask because of a discovery I made during research is that while being poisonous to the central nervous system, methanol is a natural endogenous compound found in normal, healthy human individuals.</p>
<p>One study found a mean of 4.5 ppm in the exhaled breath of the subjects. <a href="https://iopscience.iop.org/article/10.1088/0967-3334/27/7/007" rel="nofollow noreferrer">https://iopscience.iop.org/article/10.1088/0967-3334/27/7/007</a></p>
| [
{
"answer_id": 97284,
"pm_score": 3,
"text": "<p>There are 100+ gas phase compounds that come from humans.</p>\n<p><a href=\"https://i.stack.imgur.com/rVEwM.jpg\" rel=\"nofollow noreferrer\"><img src=\"https://i.stack.imgur.com/rVEwM.jpg\" alt=\"enter image description here\" /></a></p>\n<p>Find other i... | [
{
"answer_id": 3176,
"pm_score": 3,
"text": "<p>The gases NO, H₂S, CO even have a function in the human body!</p>\n\n<p>Nitric oxide is produced in endothel and neurons as messenger, and in macrophages as cause of nitrosative stress for imprisoned bacteria. Hydrogen sulfide is produced in cysteine catab... |
3,192 | <p>Are "computational biology" and "bioinformatics" simply different terms for the same thing or is there a real difference?</p>
| [
{
"answer_id": 3194,
"pm_score": 6,
"text": "<p>I found <a href=\"http://rbaltman.wordpress.com/2009/02/18/bioinformatics-computational-biology-same-no/\">this</a> post by Russ Altman quite good. Below is his opinion about the two similar but distinct fields:</p>\n\n<blockquote>\n <p><strong>Computati... | [
{
"answer_id": 3193,
"pm_score": 4,
"text": "<p>I think this question is on topic here, although yes you would definitely get a lot of answers at <a href=\"http://biostars.org/\" rel=\"nofollow noreferrer\">BioStars</a>. But consider this from the <a href=\"https://biology.stackexchange.com/tags/bioinf... |
3,290 | <p>From my experience on SE sites, I believe this is the right site to ask this question under "terminology".</p>
<p>I've been trying to find out whether English has one-word verbs for "undergo mitosis" and "undergo meiosis". I haven't been able to find confirmation on Google, but my linguistic imagination is limited, and I may have failed to google the right things. </p>
<p>Could you tell me if there are such verbs in common use in biology? I mean, if such verbs exist, can I find them in modern biology books or papers? </p>
| [
{
"answer_id": 3292,
"pm_score": 3,
"text": "<p>I'm actually not sure myself. If I were to use something, I would go with \"Mitos'd\" and \"Meios'd\".</p>\n\n<p>However, you may not win over many fans, depending on the audience. If it's with students or maybe a professor, you could get away with shorten... | [
{
"answer_id": 8106,
"pm_score": 1,
"text": "<p>Mitosis as a process does not have a verb form. However, as a process, there is an adjective; you could describe cells that undergo mitosis as mitotic. </p>\n"
},
{
"answer_id": 85153,
"pm_score": -1,
"text": "<p>Was just researching your e... |
3,393 | <p>In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. Monkeys, chimpanzees, and Apes have 24 pairs (twenty-four pairs), for a total of 48. </p>
<p>What caused humans to have 46?</p>
<p>EDIT:
@TomD is right, I was asking why we have one less chromosome pair than chimpanzees (for example) [23 pairs instead of 24].</p>
| [
{
"answer_id": 3396,
"pm_score": 5,
"text": "<p>I think the OP is asking why we have <strong>one less chromosome pair</strong> than chimpanzees (for example) [23 pairs instead of 24].</p>\n\n<p>The is an abundance of evidence, as alluded to <a href=\"https://biology.stackexchange.com/a/3394/1136\">above... | [
{
"answer_id": 3394,
"pm_score": 3,
"text": "<p>@nico is right. the number of chromosomes is the result of an evolutionary timeline, puncutated by sometimes spontaneous events which shape the DNA.</p>\n\n<p>These events occur in the course of evolution:</p>\n\n<p>1) Chromosomal rearrangements. Large s... |
4,950 | <p>The social insects consist of the ants, the bees, and the termites, which live in colonies rather than living solitary.</p>
<p>But I've heard that there are some species of bee which are solitary and don't live in colonies.</p>
<p>Are there also any species anywhere of either ants or termites which are solitary?</p>
| [
{
"answer_id": 4952,
"pm_score": 4,
"text": "<p>I do not know of any solitary ants, but there are species that form very small colonies.</p>\n\n<p>One such species is <a href=\"http://en.wikipedia.org/wiki/Harpegnathos_saltator\" rel=\"nofollow\">Jerdon's Jumping Ant (<em>Harpegnathos saltator</em>)</a>... | [
{
"answer_id": 58693,
"pm_score": 2,
"text": "<p>No solitary ants have been described by scientific journals. If they had, they would be a famous exception, their ecology and survival strategy would be very interesting, to know how they rear their broods. It is mostly nectar and parasitism that makes Hy... |
5,205 | <p>Why do we think chronic inflammation can cause cancer? I know the pathway is not fully understood, but what makes scientists believe that inflammation causes cancer?</p>
| [
{
"answer_id": 5212,
"pm_score": 4,
"text": "<p>There are good epidemiological data for this.</p>\n<blockquote>\n<p>Links between cancer and inflammation were first made in the\nnineteenth century, on the basis of observations that tumours often\narose at sites of chronic inflammation and that inflammat... | [
{
"answer_id": 37324,
"pm_score": 0,
"text": "<p>Inflammation and the inflammatory response can lead to tissue damage, and these stresses at the cellular and DNA level can lead to changes in the cell's programming. One example I can think of is neutrophils and macrophages--inflammatory cells--releasing ... |
5,217 | <p>Modern human beings, especially women, cut their armpit hair. It seems to me the armpit hair is trivial/useless. Shortly speaking, what is the armpit hair for?</p>
| [
{
"answer_id": 5247,
"pm_score": 5,
"text": "<p>I have been trying to read up a bit on this. I started out looking on <a href=\"http://en.wikipedia.org/wiki/Underarm_hair\">wikipedia</a> and it seems there are three hypotheses which are not necessarily mutually exclusive.</p>\n\n<p>1.Aid the wicking of ... | [
{
"answer_id": 5225,
"pm_score": 2,
"text": "<p>The explanation I heard from the documentary called \"Curiosity: World's Dirtiest Man\" is that armpit hairs allows for the growth of microbes which allow for the production of smell. This smell is useful for the attraction of mates in primates (although t... |
5,361 | <p>More specifically, is nicotine in the concentrations that smokers receive when smoking cigarettes toxic? I know that in great enough concentrations it can be toxic (but then, so can just about anything else, including oxygen) and I know that in plants it is used as a defense against insects and can even be used as an insecticide. However, it has always been my understanding that nicotine is irrelevant as far as the harmful effects of smoking go. </p>
<p>I recently had a conversation with another biologist who had just quit smoking and had done quite a bit of research on the subject. He said that nicotine itself is in fact bad for you and, therefore, that tobacco-less alternatives to cigarettes (such as electronic cigarettes) are still harmful <strong>because of the nicotine alone</strong>. </p>
<p>Does anyone have any more information on this? Perhaps some references? Or, even better, a detailed explanation of the pathways involved? Again, I stress, not about nicotine's toxicity in general but about its harmful effects on vertebrates (preferably human) at the kinds of concentrations one could expect to ingest when smoking.</p>
| [
{
"answer_id": 5368,
"pm_score": 5,
"text": "<p>I think its useful to say that nicotine is not very toxic to humans - cells don't die or get sick for typical smoking habits. Secondary health effects are possible, but here is a toxicological profiles. </p>\n\n<p>Nicotine is a toxin in large enough quant... | [
{
"answer_id": 5365,
"pm_score": 3,
"text": "<p>Nicotine acts as a ligand for nicotinic acetycholine receptors (nAChRs), which are ligand-gated ion channels normally activated by acetylcholine. This family of receptors is expressed in every mammalian cell (<a href=\"http://dx.doi.org/10.1038/nrc2590\">S... |
5,416 | <p>When a human being exhales CO₂, what is, by the numbers, the main source of carbon atoms exiting the body in this way? I mean what class of cells, or which tissues are the biggest on a pie chart of where carbon atoms breathed out in the form of CO₂ molecules came from?</p>
| [
{
"answer_id": 5417,
"pm_score": 6,
"text": "<p>CO<sub>2</sub> is a product of <a href=\"http://en.wikipedia.org/wiki/Cellular_respiration\">Cellular Respiration</a>, which generally takes Glucose and molecular Oxygen to produce Carbon Dioxide, water, heat, and allows ADP to be regenerated into ATP (or ... | [
{
"answer_id": 5483,
"pm_score": 2,
"text": "<p>The chemical formula for glucose is C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>. When the body needs energy, the glucose molecule is broken down to give CO<sub>2</sub> and water:</p>\n\n<p>$C_6H_{12}O_6 + 6O_2 => 6CO_2 + 6H_2O$</p>\n\n<p>Therefore, I think... |
5,458 | <p>Just had this thought occur to me.</p>
<p>If one were to take a DNA sample(or is it RNA?) of a caterpillar before it became a chrysalis, and attempt to match the sample against one taken after the chrysalis matured to a butterfly, would the two samples come up identical? </p>
| [
{
"answer_id": 5459,
"pm_score": 5,
"text": "<p>The genome (entire DNA sequence) of the butterfly would be identical to that of the caterpillar in all somatic cells. A caterpillar has the genes to produce wings, for example, however at that stage in it's development they are not 'switched on' to make t... | [
{
"answer_id": 5460,
"pm_score": 3,
"text": "<p><strong>@Rory M</strong></p>\n<p>Here is evidence for developmental genome rearrangements in <em>Hymenoptera</em>. I have emphasised the relevant section of the Abstract. It is probably premature to assume that similar changes might not happen in somatic c... |
5,621 | <p>Cows, camels, sheep, goats, etc being ruminants must chew their food repeatedly by regurgitating their food from their first stomach compartment and chewing their 'cud'. This then finer chewed material makes its way to the various stomach compartments to be digested.</p>
<p>These animals are eating plant material, the same plant material animals such as elephants, horses and hippos eat as well. However, these animals only have one stomach compartment. </p>
<ul>
<li>Why does one need a multi-compartment stomach and one does not if they are all eating the same/similar food?</li>
</ul>
| [
{
"answer_id": 5663,
"pm_score": 4,
"text": "<p>There is more difference than just the parts of plants that are eaten.</p>\n\n<p>Two of their stomachs - rumen and reticulum are not used for digesting food at all. Multiple rounds of chewing and mixing with saliva, wich result in very small particles of u... | [
{
"answer_id": 5651,
"pm_score": 0,
"text": "<p>They are not all eating the same/similar food.</p>\n\n<p>Elephants, horses and hippos are herbivores that have different diet to ruminants. Elephants, for example, have trunk to access fruits that is less difficult to digest. </p>\n"
},
{
"answer_i... |
5,623 | <p>Is every component of a virus absolutely essential for its infection and replication in a host cell? Or can you just have parts of it to cause infection? </p>
| [
{
"answer_id": 5663,
"pm_score": 4,
"text": "<p>There is more difference than just the parts of plants that are eaten.</p>\n\n<p>Two of their stomachs - rumen and reticulum are not used for digesting food at all. Multiple rounds of chewing and mixing with saliva, wich result in very small particles of u... | [
{
"answer_id": 5651,
"pm_score": 0,
"text": "<p>They are not all eating the same/similar food.</p>\n\n<p>Elephants, horses and hippos are herbivores that have different diet to ruminants. Elephants, for example, have trunk to access fruits that is less difficult to digest. </p>\n"
},
{
"answer_i... |
5,723 | <p>A well known way to have a rest of mosquitoes during camping is to stand in the fire's smoke. Moreover, I learned recently that shepherds in certain regions of Africa use the same tactic for cattle. They make smoky fires and cattle gathers in smoke to get rid of mosquitoes.</p>
<p>Why humans and cattle can stand smoke, but mosquitoes can't? Does this technique work for other kinds of insects?</p>
| [
{
"answer_id": 19028,
"pm_score": 3,
"text": "<p>There is little hard evidence on whether smoke acts as a mosquitoe repellent. A literature review done by the WHO (<a href=\"http://www.who.int/indoorair/publications/smoke_malaria/en/\" rel=\"nofollow\" title=\"Biran et al. 2008. Smoke and Malaria. World... | [
{
"answer_id": 5738,
"pm_score": -1,
"text": "<p>Mosquitoes aren't actually repelled by smoke. They are repelled by burning citronella oil. Citronella contains certain chemicals that naturally repel the dengue fever mosquito.</p>\n"
},
{
"answer_id": 5743,
"pm_score": -1,
"text": "<p>All... |
5,740 | <p>As the old joke goes, "God must have been a civil engineer. Who else would put a waste facility straight through a recreational area?"</p>
<p>But maybe it wasn't God. Is there any evolutionary reason (or background for) having the urinary duct and reproductive organs right next to each other (in both humans and many other vertebrates)?</p>
<p>To be clear, I'm not asking why <em>isn't</em> it elsewhere. I'm asking where the original "design" came from that spread everywhere.</p>
| [
{
"answer_id": 6962,
"pm_score": 4,
"text": "<p>Yes, there is.</p>\n\n<p>In order to reproduce, material has to leave one organism and enter another and, in species with internal fertilisation, the eggs need to leave later. Think back to a worm-like organism: it's basically a tube with an opening at eit... | [
{
"answer_id": 5741,
"pm_score": 3,
"text": "<blockquote>\n <p>Is there any evolutionary reason (or background for) having the urinary duct and reproductive organs right next to each other (in both humans and many other vertebrates)?</p>\n</blockquote>\n\n<p>Because it works.</p>\n\n<p>Evolution doesn'... |
6,865 | <p>I saw this refutation online of Darwin's Random Evolution Theory and cannot see any holes with the logic. Can anyone crack this simple refutation?</p>
<blockquote>
<h1>Refutation of the Theory of Random Evolution</h1>
<p>As for the theory of evolution, which says that living things evolved progressively from
mud - first organism - bacteria - fish - animals - humans through tiny
random mutations which were advantageous and naturally selected;
there's a lot to say on this. All currently living life forms appears
to be highly related, sharing the same DNA system and cell structure.
This would suggest a common first ancestor as the theory suggests (or
better yet - one Designer), however, the most obvious flaw with the
theory is that the first organism must have had highly sophisticated
intelligent design. There is a minimum requirement for even the most
primitive possible life form, without which it could not possibly
survive.</p>
<p>Minimum Requirements for First Organism</p>
<ol>
<li><p>The first organism must have a system of producing and/or sourcing energy along with subsystems of distribution and management
of that energy which interact and work together, otherwise it cannot
power critical tasks such as reproduction.</p></li>
<li><p>It must have a system of reproduction which necessitates pre-existing subsystems of information storage (DNA), information
copying, and information reading/processing which interact with each
other and work together. This reproductive system is dependent on a
power source, so it must be coordinated with the power system. The
reproductive system must also copy/rebuild all critical infrastructure
such as the power system and the reproduction system along with the
"circuitry" and feedback mechanisms between them, otherwise the child
organism will be dead..</p></li>
<li><p>It must have a growth system, otherwise the organism will reduce itself every time it reproduces and vanish after a few generations.
This growth system necessitates subsystems of ingestion of materials
from the outside world, processing of those materials, distribution,
and absorption of those materials to the proper place, building the
right thing at the right place and in the right amount. It must also
have an expulsion system for waste materials.</p>
<p>The growth system must also be coordinated with the reproduction system. Otherwise, if the reproduction trigger happens faster than the
growth, it will reduce size faster than it grows in size and vanish
after a few generations. The growth system also requires connection to
the power infrastructure to perform its tasks.</p></li>
<li><p>All the "circuitry", signaling, and feedback infrastructure which allows the different systems and subsystems to coordinate
together and work together must be in place before the organism can
"come alive". The reproduction system won't work without coordination
with the growth and power systems. Likewise, the power system by
itself is useless without the growth and reproduction systems and
cannot survive. Only when all the "circuitry", etc. is in place and
the power is turned on is there hope for the hundreds of
interdependent tasks to start working together. Otherwise, it is like
turning on a computer which has no interconnections between the power
supply, CPU, memory, hard drive, video, operating system, etc -
nothing to write home about.</p></li>
<li><p>We assume it originated in water since gas is too unstable and solid is too static. If so, the organism must be contained by some
kind of membrane otherwise its precious contents will drift away in
the water due to natural diffusion or drifting of water due to
temperature variations in the water from sunlight, etc. or from heat
generated through its own power, or wind, moon, etc. If so, this makes
the assembly of such an organism more problematic, since it would need
to be closed shut before it can build itself in a stable way. Yet, to
build itself it would need to be open for a long time until all
systems are built and interconnected.</p></li>
</ol>
<p>From the above minimum requirements it is clear that the simplest
possible surviving organism is by no means simple. You would need
thousands of different proteins/lipids etc., in the right proportions,
all intricately folded and actively interacting with each other and
with sophisticated organelles. Contemplate this and you will see the
necessary complexity of this primitive organism is far more
sophisticated than anything modern technology has ever produced. Even
the most sophisticated Intel CPU is mere child's play compared with
the design of such an organism.</p>
</blockquote>
| [
{
"answer_id": 6874,
"pm_score": 5,
"text": "<p>I like @5th 's answer but I thought it might be worthwhile to clarify on some points and pull the logic out a bit more. </p>\n\n<p>First there is some contesting the overall logic that it assumes all these <em>qualities of life are showing up at once</em>... | [
{
"answer_id": 6870,
"pm_score": 4,
"text": "<p>(A few words about your source: it's little use to come a serious site about science and quote sources whose objective is to prove the existence of god. If you want to learn more about the beauty of life and the theory of evolution, I suggest you read the ... |
7,019 | <p>For instance, I realise being able to absorb simple sugars in the mouth is pivotal in the rapid action of oral glucose gel. Thus I was wondering what nutrients in general can be absorbed directly within the mouth, and <em>at what speed</em>?</p>
| [
{
"answer_id": 9143,
"pm_score": 4,
"text": "<p>Quite a bit can be absorbed through the mouth. Most commonly, starches are broken down to maltose (two glucose molecules formed by a condensation reaction) and are easily absorbed by the bloodstream. </p>\n\n<p>A lot of other factors balance into this, ie ... | [
{
"answer_id": 8470,
"pm_score": -1,
"text": "<p>Many vitamins are absorbed in mouth. Even spraying vitamins will help you overcome vitamin deficiency.\nEven some drugs can be absorbed directly into mouth.</p>\n"
},
{
"answer_id": 10399,
"pm_score": 2,
"text": "<p>The mouth or the oral c... |
7,023 | <p>The most <a href="http://en.wikipedia.org/wiki/Transformation_%28genetics%29#Plants" rel="nofollow">common method to transform plants</a> is by soaking plant tissue in cultures of agrobacteria (<a href="http://en.wikipedia.org/wiki/Agrobacterium" rel="nofollow">this is not their current classification</a>) which transfer DNA into the plants. </p>
<p>Is lateral gene transfer ability like this found a lot in nature? Is <em>agrobacterium tumificans</em> especially good at this or is its use in plant genetics only because this strain is well studied?</p>
<p>Is a method like this used for animal cells at all? </p>
| [
{
"answer_id": 9143,
"pm_score": 4,
"text": "<p>Quite a bit can be absorbed through the mouth. Most commonly, starches are broken down to maltose (two glucose molecules formed by a condensation reaction) and are easily absorbed by the bloodstream. </p>\n\n<p>A lot of other factors balance into this, ie ... | [
{
"answer_id": 8470,
"pm_score": -1,
"text": "<p>Many vitamins are absorbed in mouth. Even spraying vitamins will help you overcome vitamin deficiency.\nEven some drugs can be absorbed directly into mouth.</p>\n"
},
{
"answer_id": 10399,
"pm_score": 2,
"text": "<p>The mouth or the oral c... |
7,400 | <p>I know from school, that all live on the Earth need <strong>bacteria</strong> as low-level "<em>machines</em>" that break down/extract/convert/produce chemical elements and combinations, other high-level organisms needed. But it is a natural way.</p>
<p>But is it possible to have a world with plants (without mammals or microorganisms and <strong>without bacteria</strong>) that could exist in the long term. Saying the atmosphere of these world has already enough nitrogen, oxygen and CO<sub>2</sub>, and of course there is water.</p>
<p>What could break this artificially created world with such conditions (say the world created not from low-level living structures)?
Could bacteria emerge in the world?</p>
| [
{
"answer_id": 7409,
"pm_score": 4,
"text": "<p>This is the sort of question that should be considered from more than one perspective. Since this is speculation, take it as a given that there is a lot of 'what if' here. </p>\n\n<p>I doubt most animals and plants can do entirely without bacteria - as yo... | [
{
"answer_id": 10954,
"pm_score": 2,
"text": "<p>Think of it this way: Life always goes uphill, from less developed to more adapted, better at surviving and reproducing.</p>\n\n<p>Early life would be a basic mechanism, trivial in nature, that under the right conditions would kind of replicate itself (ki... |
7,718 | <p>I'm writing a little article and need any information about how human vision works and latest
technologies and discoveries around. Actually its not a professional article. Its for a group of my friends.</p>
<p>In fact I'm looking for any possible way to make someone ACTUALLY see when their eyes are closed. I don't know maybe convince some of brain cells that a real pulse is coming from eyes, but in reality its coming from a computer; or something like that.</p>
<p>I call it a virtual vision, myself.</p>
<p>Do you guys know if there's any professional article, discoveries or technologies available about this topic?
I'm very very interested in this topic by the way.</p>
| [
{
"answer_id": 7724,
"pm_score": 4,
"text": "<p>Yes, this is most certainly possible and already being done. As long as the visual cortex of the brain (in the occipital lobe, i.e. at the back of your head) is functional, the correct stimulation will produce visual perception.</p>\n\n<p>In cases of blind... | [
{
"answer_id": 7722,
"pm_score": 0,
"text": "<p>I am not an expert on this subject, but essentially what you would need is to have a machine interface directly with neurons.</p>\n\n<p>Neuro-mechanical interface is something which interests many scientists but unfortunately we are only at extremely early... |
7,758 | <p>So I came across something terribly amazing today, that is, a video showing this species of peacock-spider, that literally, <a href="http://www.youtube.com/watch?v=d_yYC5r8xMI" rel="nofollow">transforms into a human face waving his arms about</a>. </p>
<p>What could have possibly given rise to this?</p>
<p>I can understand the arms waving around, but why the uncanny human-face template, complete with eyes, nose, mouth, etc. </p>
<p>I do not believe this to be a case of anthropomorphism on my part, (seeing what I am familiar with), because I cannot imagine any other natural case where such symmetry in a pattern would closely resemble a human face. </p>
<p>Would appreciate any explanation. Thanks! </p>
| [
{
"answer_id": 7759,
"pm_score": 5,
"text": "<p>I think this really is just a case of what you refer to in your question as anthropomorphism. We are very, very good at seeing faces. <a href=\"http://www.cracked.com/quick-fixes/the-3-most-terrifying-faces-drawn-by-nature/\">Here are some more examples</a... | [
{
"answer_id": 7761,
"pm_score": 1,
"text": "<p>In part, the way the spider resembles a human face is due to <a href=\"http://en.wikipedia.org/wiki/Symmetry_in_biology#Bilateral_symmetry\" rel=\"nofollow\">bilateral symmetry</a> in the body shape and coloring of the spider. Bilateral symmetry evolved ea... |
8,176 | <p>Do organisms exist that are able to live indefinitely if they are not killed by external factors?</p>
<p>Under external factors I would consider things like predators and natural disaster but not illness by bacteria for example.</p>
| [
{
"answer_id": 8179,
"pm_score": 5,
"text": "<p>I now found this Wikipedia article on <a href=\"http://en.wikipedia.org/wiki/Biological_immortality\">biological immortality</a>. It's pretty much what I was looking for.</p>\n\n<p>Wikipedia describes the phenomenon as follows:</p>\n\n<blockquote>\n <p>Bi... | [
{
"answer_id": 9168,
"pm_score": 4,
"text": "<p>Yes. The Bristlecone Pine, <em>Pinus longaeva</em>, is one example. This species boasts the oldest individual living organisms, and also has been convincingly argued by <a href=\"http://dx.doi.org/10.1016/S0531-5565%2800%2900234-5\">Lanner and Connor (2001... |
8,180 | <p>One rate-limiting step of glycolysis is the conversion of Fructose-6-Phosphate (Fruc-6-P) to Fructose-1,6-Bisphosphate (Fruc-1,6-BP), catalysed by Phosphofructokinase 1 (PFK 1). The reaction involves hydrolysing one ATP to ADP.</p>
<p>The reverse reaction of gluconeogenesis is catalysed by Fructose-Bisphosphatase (FBP). This reaction uses 1 H<sub>2</sub>O for hydrolysis and yields 1 phosphate (P<sub>i</sub>).</p>
<p>One would expect the cell to be utilising only one of the two reactions at any one time, either to break down glucose or to generate it. However, the case is commonly that both reactions are taking place simultaneously in an equilibrium [ref 'Biochemistry', Voet & Voet, 4th ed., 628-629 (Section 17-4-F-f,g,h,(i))], cycling Fruc-1,6-BP to no apparent benefit, at the expense of valuable ATP.</p>
<p>What is the purpose of such futile cycles?</p>
| [
{
"answer_id": 8179,
"pm_score": 5,
"text": "<p>I now found this Wikipedia article on <a href=\"http://en.wikipedia.org/wiki/Biological_immortality\">biological immortality</a>. It's pretty much what I was looking for.</p>\n\n<p>Wikipedia describes the phenomenon as follows:</p>\n\n<blockquote>\n <p>Bi... | [
{
"answer_id": 9168,
"pm_score": 4,
"text": "<p>Yes. The Bristlecone Pine, <em>Pinus longaeva</em>, is one example. This species boasts the oldest individual living organisms, and also has been convincingly argued by <a href=\"http://dx.doi.org/10.1016/S0531-5565%2800%2900234-5\">Lanner and Connor (2001... |
8,236 | <p>I couldn't help but notice just how non-descriptive the gene names that modern genetics is using. Currently I'm reading "The new science of Evo Devo" by Sean B. Carroll and here are some examples of gene names used:</p>
<ul>
<li>Fzrb</li>
<li>Krox 20</li>
<li>Hoxa2, Hoxb4</li>
<li>ZPA</li>
<li>FGF8</li>
<li>sonic hedgehog</li>
</ul>
<p>While these names identify genes uniquely, they do very little to express what and where the gene does, or how it is related to other genes (While FGF8 may be related to FGF7, it's relationship to XYZ10 is not obvious).</p>
<p>I get the need to uniquely identify genes , and <strong>the book is an example of just how hard it is to presently write about a lot of genes at once.</strong> The author creates a picture of what's going on, but the gene names get in the way. Even in cases where a gene has a semi-descriptive name, like "eyeless", the reader has to remember that it's actually the gene responsible for eye formation.</p>
<p><strong>Are there are any efforts underway to systematize or name genes for a given organism in an expressive manner?</strong></p>
<p>As a programmer, I write code for a living, and having descriptive names makes it easier to look at someone else's code, read about code and even discuss it with novices. For example:</p>
<ul>
<li>initializeDataModel</li>
<li>createViewHierarchy</li>
<li>userDidSelectLayerAtIndex</li>
</ul>
<p>Modern programming tools make using descriptive names easier, because of autocomplete - typing in the first few letters of a programming structure completes the rest. Even google has a list of autocomplete suggestions. </p>
<p>We are all familiar with the Internet, where biology.stackexchange.com/questionname resolves into a specific page. Stackexchange is the site we are visiting, and Biology is a subset of that site. There are other biology websites, but biology.stackexchange.com uniquely identifies this site. The use of "biology" in the address gives readers a general idea of what the site is about and relates it to other biology sites. Our web browsers resolve the address into a proper string of bytes and get the right page. <strong>What if we name genes like like</strong></p>
<ul>
<li>com.drosophila.eyeformation</li>
<li>com.chicken.limb.structure.ZPA</li>
<li>com.human.development.geometry/XYZ10</li>
</ul>
<p>,and whatever technology we use would actually resolve that descriptive name into a gene or a series of gene interactions? </p>
| [
{
"answer_id": 8239,
"pm_score": 3,
"text": "<p>Many gene names are descriptive, e.g. DRD1: dopamine receptor D1, TOP2A: DNA topoisomerase 2-alpha, or PTGS1: prostaglandin G/H synthase 1. These are examples of genes that have a clearly defined main function.</p>\n\n<p>The genes you listed are involved i... | [
{
"answer_id": 8238,
"pm_score": 1,
"text": "<blockquote>\n <p>Are there are any efforts underway to systematize or name genes for a given organism in an expressive manner?</p>\n</blockquote>\n\n<p>As you observed, the genes are named by their discoverers and some genes usually have anecdotes behind th... |
8,244 | <p>I'm a biotechnology student and I have to write a sort of non-experimental thesis (30 pages long) within the end of a three years study.</p>
<p>I'm very interested in the "<a href="http://en.wikipedia.org/wiki/Systems_biology" rel="nofollow">systems biology</a>" field and I'm searching good (innovative) and recent (max 3-4 years old) articles about this subject, but unfortunately I've found my research more difficult than I expected.</p>
<p>I'd like to focus on not immediate/easy articles and possibly containing new and promising approaches.</p>
<p>Does anybody have suggestions?</p>
<p>PS: it all started from <a href="http://www.youtube.com/watch?v=Z__BHVFP0Lk" rel="nofollow">Uri Alon's great lessons on YouTube</a>.</p>
| [
{
"answer_id": 8239,
"pm_score": 3,
"text": "<p>Many gene names are descriptive, e.g. DRD1: dopamine receptor D1, TOP2A: DNA topoisomerase 2-alpha, or PTGS1: prostaglandin G/H synthase 1. These are examples of genes that have a clearly defined main function.</p>\n\n<p>The genes you listed are involved i... | [
{
"answer_id": 8238,
"pm_score": 1,
"text": "<blockquote>\n <p>Are there are any efforts underway to systematize or name genes for a given organism in an expressive manner?</p>\n</blockquote>\n\n<p>As you observed, the genes are named by their discoverers and some genes usually have anecdotes behind th... |
8,272 | <p>How long can a naked human survive at the surface of the Mars planet?</p>
<p>For instance, let's say a worker's base takes fire while he sleeps, the building is totally ablaze and he can do nothing but <strong>run to the emergency building 200 meters away</strong> without any respiratory equipment, pressure suit, UV protections or anything.</p>
<p>Maybe a human could survive for a rather long time, and <a href="http://en.wikipedia.org/wiki/Apnea" rel="noreferrer">apnea time</a> is the real limiting factor?</p>
<p><a href="http://en.wikipedia.org/wiki/Climate_of_Mars" rel="noreferrer">Climate</a>:</p>
<ul>
<li>Temperature: 27 °C to −50 °C (base is at a rather warm location, on Equator)</li>
<li>Pressure: 0.006 bar (Earth: 1 bar)</li>
</ul>
| [
{
"answer_id": 14423,
"pm_score": 5,
"text": "<p>Long story short, the astronaut probably wouldn't make it, and would first loose consciousness then suffocate.</p>\n\n<p>There is a lot of myth and hollywood dramatization regarding this kind of thing. Here are some:</p>\n\n<ol>\n<li><strong>You will expl... | [
{
"answer_id": 8274,
"pm_score": 3,
"text": "<p>Less then a minute breathing in the atmosphere (and a very painful death). <a href=\"http://en.wikipedia.org/wiki/Atmosphere_of_Mars\" rel=\"noreferrer\">Mars' atmosphere</a> is >95% CO<sub>2</sub> with only trivial O<sub>2</sub>. These are atmospheric con... |
8,279 | <p>Can humans live without eating food, just by drinking water? How long can we survive just by drinking water everyday?</p>
| [
{
"answer_id": 8283,
"pm_score": 5,
"text": "<p>About 52 to 74 days according to <a href=\"http://en.wikipedia.org/wiki/Hunger_strike#Medical_view\"><code>hunger strike</code> wiki page</a>.</p>\n\n<p>This wiki page bases its data on <a href=\"http://en.wikipedia.org/wiki/1981_Irish_hunger_strike#Partic... | [
{
"answer_id": 8280,
"pm_score": 3,
"text": "<p>This <a href=\"http://mostextreme.org/longest_without_food.php\">would vary a LOT depending on the amount of stored fat, previous diet, the weather and even the water drunk</a>. Weeks though there is a good chance that a <a href=\"http://en.wikipedia.org/... |
8,449 | <p>I have learned that first a protocell came to exist and its characteristics came to be passed on by genetic material. So how come genes for all the activities come to incorporate into genetic material? Did genetic material come first and random sequences made random proteins that were used to make cells ?</p>
| [
{
"answer_id": 9963,
"pm_score": 2,
"text": "<p>Well.. This is a tough question (Something that has bugged me for years and still doing so). I don't fully agree that replicative potential came first. This is just my opinion based on some reasoning and I dont really have any reference. </p>\n\n<p>If you ... | [
{
"answer_id": 8451,
"pm_score": 0,
"text": "<p>The general theory is RNA came first, then DNA. Both are able to replicate with simple changes in temperature (see polymerase chain reaction). So if we imagine a world with nucleotides making RNA, the idea is the survival of the fittest RNA. RNA for exampl... |
8,513 | <p>When neuron animations are displayed, there are frequently seen neurons, axons arranged in a lattice with a lot of empty space between. I'm interested if there is indeed empty space in the brain, or if it is filled with some sort of fluid? I've checked an article on <a href="http://en.wikipedia.org/wiki/Cerebrospinal_fluid" rel="nofollow">cerebrospinal fluid</a> but am not sure that it is present all throughout the brain.</p>
<p>The reason I'm asking is that I'm thinking of neurotransmitters- they are released in synapses, but I'm not sure how they stay there - are they suspended in some liquid as well?</p>
| [
{
"answer_id": 8515,
"pm_score": 4,
"text": "<p>Not so empty, actually.</p>\n\n<p>The human brain has a mass of ~1.5kg, and volume ~1200cc (a little bigger for men, a little smaller for women). So is heavier than water by a good margin.</p>\n\n<p>While it has Cerebrospinal fluid, that only occupies the ... | [
{
"answer_id": 8514,
"pm_score": 2,
"text": "<p>Apologies for just referencing Wikipedia, but this is a very old bit of science.</p>\n\n<p>The neuron gap junction - the point where the axon touches the next cell over - <a href=\"http://en.wikipedia.org/wiki/Gap_junction#Structure\" rel=\"nofollow\">is 4... |
8,518 | <p>Is there a small chance that in sexual reproduction a new allele forms in the off-spring that was not present in either of the parents, or are the alleles in the offspring always from at least one of the parents? </p>
<p>Is new genetic information ever created during sexual reproduction, or only through mutations during an organisms life time?</p>
| [
{
"answer_id": 8524,
"pm_score": 4,
"text": "<p>Homologous Recombination not only shuffles different mutations together, but similar sequences near each other from gene duplication events and from regions with highly repetitive sequences can r<a href=\"http://en.wikipedia.org/wiki/Non_allelic_homologous... | [
{
"answer_id": 8520,
"pm_score": 2,
"text": "<p>Many mutations occur during DNA replication (or when a mutagen is around, but that also largely affects replication).</p>\n\n<p>Mutations occurring \"during sexual reproduction\" might occur during gametogenesis, when the eggs and sperm are developing in t... |
8,759 | <p>The male to female ratio in autism spectrum disorder is around 4:1. However it seems ASD is not a simple X-linked disorder. </p>
<p>Then how is it possible males are more susceptible than females, if the causal genes are located in autosomes? </p>
| [
{
"answer_id": 8765,
"pm_score": 4,
"text": "<p>As the father of two sons with diagnoses of ASD, I think that it is best to think in terms of an extended spectrum which encompasses 'normal' people. We are all somewhere on this spectrum, but there is a threshold zone around where we cross from \"normal\"... | [
{
"answer_id": 8761,
"pm_score": 2,
"text": "<p>Males are more likely to develop ASD, but affected females tend to be more severely impaired. Why this occurs is an area of active research.</p>\n\n<p>However, to address your question, there is a <a href=\"http://stm.sciencemag.org/content/2/49/49ra68.abs... |
9,095 | <p>Firstly I could do with a brief description of mitochondrial DNA. How does the structure of DNA in mitochondria compare to animal DNA (for the sake of simplicity let's say human - some animals might have unusual DNA structure) and what living organism is the mitochondrial genome most akin to? (Circular like bacteria maybe?) and are the mitochondria within a single human homogenous?</p>
<p>Secondly, and most importantly to my aim, does the mitochondrial genome recombine in anyway? Is the process of recombination affected by its structure? Are there any patterns/rules in mitochondrial recombination? Is there DNA transfer between mitochondria which could have a similar effect?</p>
<p>I am trying to think about how male deleterious alleles can spread differently in diverged populations given potential recombination to female beneficial (or recombination away from female deleterious mutations). </p>
| [
{
"answer_id": 9099,
"pm_score": 3,
"text": "<p>Mitochondrial DNA is circular, like bacterial DNA, and around 16.6 Kb long. It codes for 37 genes in total but the majority of these are simply the machinery for gene expression (curiously, mitochondria have a slightly different codon->amino acid translati... | [
{
"answer_id": 9106,
"pm_score": 0,
"text": "<p>Addition to Jack Adley's answer:</p>\n\n<p>Evolutionarily, mitochondria are thought to be descended from α-proteobacterium (<em>Rickettsia</em> are also descendants of this bacterium). </p>\n\n<p>There are evidences that <a href=\"http://www.nature.com/nat... |
9,107 | <p>What causes autism?
By this <strong>I don't mean what is to blame</strong> i.e. Vaccines, Gluten or Pharmaceuticals etc.. I mean <strong>what exactly is happening in the brain</strong> to cause the autistic behaviors such as little to no communication skills, regression of skills around age 3, hand flapping etc..
I see a lot of research looking for something to blame however I see little to no research on identifying the physical causes or links (maybe I'm not using the correct search terms).</p>
| [
{
"answer_id": 9166,
"pm_score": 4,
"text": "<p><a href=\"http://en.wikipedia.org/wiki/Fragile_X_syndrome\" rel=\"noreferrer\">Fragile X syndrome</a> is a genetic disorder which is highly <a href=\"http://dept.wofford.edu/neuroscience/neuroseminar/pdfFall2011/5-fragileX-autism.pdf\" rel=\"noreferrer\">r... | [
{
"answer_id": 9108,
"pm_score": 2,
"text": "<p>While still not entirely clear as to what causes autism, there is a growing body of research (as jonsca said), and a model is being developed.</p>\n\n<p>A suggested explanation from <a href=\"http://www.autism.net.au/Autism_causes.htm\" rel=\"nofollow\">\"... |
9,119 | <p>I've recently read a little on Wikipedia about genetics, but I can't find a direct answer to this question.</p>
<p>My rough understanding is this:</p>
<ul>
<li>Both males and females have pairs of chromosomes, one copy from each parent</li>
<li>Both produce gametes (eggs in females, sperm in males)</li>
<li>The gamete is produced during something called 'meiosis' to take only one set of genes</li>
</ul>
<p>What I can't find an answer to though is whether that selection is completely random, such that every chromosome in a gamete has an equally likely chance of being taken from the male parent set and the female parent set.</p>
<p>Another way of putting it, perhaps: Would the range of 100% male parent to 100% female parent chromosome selection in the gamete be a binomial distribution?</p>
<p>My background is computing, so please assume very little knowledge of biology.</p>
| [
{
"answer_id": 9123,
"pm_score": 4,
"text": "<p>Other answers are correct in their own terms, but because of homologous recombination during meiosis, the idea of maternal and paternal chromosomes becomes meaningless. Any chromosome in a gamete will be a mosaic of the maternal and paternal versions. In t... | [
{
"answer_id": 9121,
"pm_score": 0,
"text": "<p>Yes, every chromosome in gamete has an equal probability of being taken from the male parent set and the female set.</p>\n"
},
{
"answer_id": 9122,
"pm_score": 1,
"text": "<p>Yes, for all intents and purposes, the assorting of chromosomes d... |
9,120 | <p>DNA replication is more accurate than transcription (or RNA replication) because mechanisms exist for proof-reading and repair of DNA, but not for RNA.
Consider a segment of a DNA strand, AGTC. Its complement is GACT. Now suppose its complement is mutated to TACT — the DNA repair system will replace the wrong T by G. Why isn’t A in the original strand replaced by C? How does the system determine that the first strand is correct and its complement is incorrect? </p>
| [
{
"answer_id": 9133,
"pm_score": 3,
"text": "<p>The reason the fact it isn't realistic is important. DNA repair machinery works by repairing common errors that occur due to common mutational pathways. The enzymes are specific for this, for example one particular enzyme targets mutations caused by UV and... | [
{
"answer_id": 9124,
"pm_score": 1,
"text": "<p>Your specific scenario is not realistic, thymine is a pyrimidine base while guanine is a purine base. They are very different chemically and can't spontaneously convert into each other. So this is a type of damage that only occurs during the replication of... |
9,154 | <p>A person wih blood group O is called a Universal Donor. Well, his plasma contains antibodies A and B. During blood donation, if blood group O is given to a person with blood group A (since blood group O can be donated to all the blood groups) then wouldn't the antibodies of the donor with blood group O harm the recipient?
Although nowadays doctors prefer giving blood having 100 percent compatibility...</p>
| [
{
"answer_id": 9158,
"pm_score": 4,
"text": "<p>The key feature of type O blood as \"universal donor\" is that the incoming red blood cells have neither A nor B antigens and so the resident antibodies (anti-A , anti-B) will not react with them. Since transfusions are carried out with packed red blood ce... | [
{
"answer_id": 9157,
"pm_score": -1,
"text": "<p>Since a person with blood group O does not express the A and B antigens, his blood does not contain antibodies to A and B. Therefore, it is safe to transfuse into someone with type A, B, AB, or O blood.</p>\n"
},
{
"answer_id": 21296,
"pm_scor... |
9,271 | <p>I remember that in Michael Crichton's novel <a href="http://en.wikipedia.org/wiki/Jurassic_Park_%28novel%29">Jurassic Park</a>, Tyrannosaurus Rex was supposed to have movement based vision. (Of course, that is a novel and not a scientific text.) </p>
<p>I have also noticed while feeding chickens, that they behave differently when they see me adding the food for them into the container as opposed to leaving it there for them when they cannot see me. (But this can be explained easily by different reasons, for example they are used to human as a source of their food, so they naturally go close to them.)</p>
<p>So my question is:</p>
<p><strong>Are there some kinds of animals who have primarily movement based vision? If yes, which animals are examples for this?</strong></p>
<hr>
<p>The Michael Crichton's novel has been widely discussed online, I found for example <a href="http://jurassicpark.wikia.com/wiki/Tyrannosaurus_rex#Eyesight_Debate">this</a> and several answers at <a href="http://answers.yahoo.com/question/index?qid=20061217193648AASG0Fp">Yahoo Answers</a>. Frogs and reptiles are mentioned there. </p>
| [
{
"answer_id": 9280,
"pm_score": 4,
"text": "<p>I think \"movement-based vision\" is perhaps a bit of a misnomer. Ultimately, all vision is <a href=\"https://www.ncbi.nlm.nih.gov/pubmed/21092350\" rel=\"nofollow\">contrast-based, depending on integrating signals from ON and OFF bipolar cells</a>. It see... | [
{
"answer_id": 9275,
"pm_score": 1,
"text": "<p>There certainly are many adaptations in the light receptors in the eyes that enhance <a href=\"http://www.springerreference.com/docs/html/chapterdbid/318221.html\" rel=\"nofollow\">contrast, color sensing, color discrimination as well as feature and moveme... |
9,739 | <p>Reading this <a href="https://biology.stackexchange.com/questions/5007/how-is-evolution-possible-in-contemporary-humans">question</a> of the stack exchange got me thinking. I believe human evolution is an ongoing process and will not stop. Are there any predictions/theories about the phenotypes and genotypes of humans in the future? and how they may differ in a few thousand years compared to present day?</p>
<p>I remember watching a youtube video and in the video the user predicts that there will be two branches of human species; a short dwarf like species and a much taller species. I'm still skeptical about this claim. Is there any evidence to back it up?</p>
<p>One could argue that modern medicine is preventing natural selection. How will this effect human evolution?</p>
| [
{
"answer_id": 9740,
"pm_score": 4,
"text": "<p>Its pretty much impossible to predict what will happen in the evolution of species. Evolution is a parallel search with millions (or in the case of humans 8+ billion) of threads. Our adaptive capacities have never been fully understood and will always su... | [
{
"answer_id": 9756,
"pm_score": 1,
"text": "<p>It is an interesting question, and I definitely agree with shigeta's question about medical technologies enabling the transmission of certain negative traits that would probably otherwise be less frequent.</p>\n\n<p>Remember, evolution is really just a num... |
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