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The number, size, shape, and banding pattern of chromosomes make them easily identifiable in a karyogram and allow for the assessment of many chromosomal abnormalities. Disorders in chromosome number, or aneuploidies, are typically lethal to the embryo, although a few trisomic genotypes are viable. Because of X inactiv... | https://openstax.org/books/concepts-biology/pages/7-chapter-summary |
alternation of generations : a life-cycle type in which the diploid and haploid stages alternate | https://openstax.org/books/concepts-biology/pages/7-key-terms |
aneuploid : an individual with an error in chromosome number; includes deletions and duplications of chromosome segments | https://openstax.org/books/concepts-biology/pages/7-key-terms |
autosome : any of the non-sex chromosomes | https://openstax.org/books/concepts-biology/pages/7-key-terms |
chiasmata : (singular =chiasma) the structure that forms at the crossover points after genetic material is exchanged | https://openstax.org/books/concepts-biology/pages/7-key-terms |
chromosome inversion : the detachment, 180° rotation, and reinsertion of a chromosome arm | https://openstax.org/books/concepts-biology/pages/7-key-terms |
crossing over : (also, recombination) the exchange of genetic material between homologous chromosomes resulting in chromosomes that incorporate genes from both parents of the organism forming reproductive cells | https://openstax.org/books/concepts-biology/pages/7-key-terms |
diploid-dominant : a life-cycle type in which the multicellular diploid stage is prevalent | https://openstax.org/books/concepts-biology/pages/7-key-terms |
euploid : an individual with the appropriate number of chromosomes for their species | https://openstax.org/books/concepts-biology/pages/7-key-terms |
fertilization : the union of two haploid cells typically from two individual organisms | https://openstax.org/books/concepts-biology/pages/7-key-terms |
gametophyte : a multicellular haploid life-cycle stage that produces gametes | https://openstax.org/books/concepts-biology/pages/7-key-terms |
germ cell : a specialized cell that produces gametes, such as eggs or sperm | https://openstax.org/books/concepts-biology/pages/7-key-terms |
haploid-dominant : a life-cycle type in which the multicellular haploid stage is prevalent | https://openstax.org/books/concepts-biology/pages/7-key-terms |
interkinesis : a period of rest that may occur between meiosis I and meiosis II; there is no replication of DNA during interkinesis | https://openstax.org/books/concepts-biology/pages/7-key-terms |
karyogram : the photographic image of a karyotype | https://openstax.org/books/concepts-biology/pages/7-key-terms |
karyotype : the number and appearance of an individuals chromosomes, including the size, banding patterns, and centromere position | https://openstax.org/books/concepts-biology/pages/7-key-terms |
life cycle : the sequence of events in the development of an organism and the production of cells that produce offspring | https://openstax.org/books/concepts-biology/pages/7-key-terms |
meiosis : a nuclear division process that results in four haploid cells | https://openstax.org/books/concepts-biology/pages/7-key-terms |
meiosis I : the first round of meiotic cell division; referred to as reduction division because the resulting cells are haploid | https://openstax.org/books/concepts-biology/pages/7-key-terms |
meiosis II : the second round of meiotic cell division following meiosis I; sister chromatids are separated from each other, and the result is four unique haploid cells | https://openstax.org/books/concepts-biology/pages/7-key-terms |
monosomy : an otherwise diploid genotype in which one chromosome is missing | https://openstax.org/books/concepts-biology/pages/7-key-terms |
nondisjunction : the failure of synapsed homologs to completely separate and migrate to separate poles during the first cell division of meiosis | https://openstax.org/books/concepts-biology/pages/7-key-terms |
polyploid : an individual with an incorrect number of chromosome sets | https://openstax.org/books/concepts-biology/pages/7-key-terms |
recombinant : describing something composed of genetic material from two sources, such as a chromosome with both maternal and paternal segments of DNA | https://openstax.org/books/concepts-biology/pages/7-key-terms |
reduction division : a nuclear division that produces daughter nuclei each having one-half as many chromosome sets as the parental nucleus; meiosis I is a reduction division | https://openstax.org/books/concepts-biology/pages/7-key-terms |
somatic cell : all the cells of a multicellular organism except the gamete-forming cells | https://openstax.org/books/concepts-biology/pages/7-key-terms |
sporophyte : a multicellular diploid life-cycle stage that produces spores | https://openstax.org/books/concepts-biology/pages/7-key-terms |
synapsis : the formation of a close association between homologous chromosomes during prophase I | https://openstax.org/books/concepts-biology/pages/7-key-terms |
tetrad : two duplicated homologous chromosomes (four chromatids) bound together by chiasmata during prophase I | https://openstax.org/books/concepts-biology/pages/7-key-terms |
translocation : the process by which one segment of a chromosome dissociates and reattaches to a different, nonhomologous chromosome | https://openstax.org/books/concepts-biology/pages/7-key-terms |
trisomy : an otherwise diploid genotype in which one entire chromosome is duplicated | https://openstax.org/books/concepts-biology/pages/7-key-terms |
X inactivation : the condensation of X chromosomes into Barr bodies during embryonic development in females to compensate for the double genetic dose | https://openstax.org/books/concepts-biology/pages/7-key-terms |
Working with garden pea plants, Mendel found that crosses between parents that differed for one trait produced F1offspring that all expressed one parentâs traits. The traits that were visible in the F1generation are referred to as dominant, and traits that disappear in the F1generation are described as recessive. Whe... | https://openstax.org/books/concepts-biology/pages/8-chapter-summary |
When true-breeding, or homozygous, individuals that differ for a certain trait are crossed, all of the offspring will be heterozygous for that trait. If the traits are inherited as dominant and recessive, the F1offspring will all exhibit the same phenotype as the parent homozygous for the dominant trait. If these heter... | https://openstax.org/books/concepts-biology/pages/8-chapter-summary |
Mendel postulated that genes (characteristics) are inherited as pairs of alleles (traits) that behave in a dominant and recessive pattern. Alleles segregate into gametes such that each gamete is equally likely to receive either one of the two alleles present in a diploid individual. In addition, genes are assorted into... | https://openstax.org/books/concepts-biology/pages/8-chapter-summary |
Alleles do not always behave in dominant and recessive patterns. Incomplete dominance describes situations in which the heterozygote exhibits a phenotype that is intermediate between the homozygous phenotypes. Codominance describes the simultaneous expression of both of the alleles in the heterozygote. Although diploid... | https://openstax.org/books/concepts-biology/pages/8-chapter-summary |
According to Mendelâs law of independent assortment, genes sort independently of each other into gametes during meiosis. This occurs because chromosomes, on which the genes reside, assort independently during meiosis and crossovers cause most genes on the same chromosomes to also behave independently. When genes are ... | https://openstax.org/books/concepts-biology/pages/8-chapter-summary |
Whether or not they are sorting independently, genes may interact at the level of gene products, such that the expression of an allele for one gene masks or modifies the expression of an allele for a different gene. This is called epistasis. | https://openstax.org/books/concepts-biology/pages/8-chapter-summary |
allele : one of two or more variants of a gene that determines a particular trait for a characteristic | https://openstax.org/books/concepts-biology/pages/8-key-terms |
codominance : in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic | https://openstax.org/books/concepts-biology/pages/8-key-terms |
continuous variation : a variation in a characteristic in which individuals show a range of traits with small differences between them | https://openstax.org/books/concepts-biology/pages/8-key-terms |
dihybrid : the result of a cross between two true-breeding parents that express different traits for two characteristics | https://openstax.org/books/concepts-biology/pages/8-key-terms |
discontinuous variation : a variation in a characteristic in which individuals show two, or a few, traits with large differences between them | https://openstax.org/books/concepts-biology/pages/8-key-terms |
dominant : describes a trait that masks the expression of another trait when both versions of the gene are present in an individual | https://openstax.org/books/concepts-biology/pages/8-key-terms |
epistasis : an interaction between genes such that one gene masks or interferes with the expression of another | https://openstax.org/books/concepts-biology/pages/8-key-terms |
F1 : the first filial generation in a cross; the offspring of the parental generation | https://openstax.org/books/concepts-biology/pages/8-key-terms |
F2 : the second filial generation produced when F1individuals are self-crossed or fertilized with each other | https://openstax.org/books/concepts-biology/pages/8-key-terms |
genotype : the underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism | https://openstax.org/books/concepts-biology/pages/8-key-terms |
hemizygous : the presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant | https://openstax.org/books/concepts-biology/pages/8-key-terms |
heterozygous : having two different alleles for a given gene on the homologous chromosomes | https://openstax.org/books/concepts-biology/pages/8-key-terms |
homozygous : having two identical alleles for a given gene on the homologous chromosomes | https://openstax.org/books/concepts-biology/pages/8-key-terms |
hybridization : the process of mating two individuals that differ, with the goal of achieving a certain characteristic in their offspring | https://openstax.org/books/concepts-biology/pages/8-key-terms |
incomplete dominance : in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype | https://openstax.org/books/concepts-biology/pages/8-key-terms |
law of dominance : in a heterozygote, one trait will conceal the presence of another trait for the same characteristic | https://openstax.org/books/concepts-biology/pages/8-key-terms |
law of independent assortment : genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur | https://openstax.org/books/concepts-biology/pages/8-key-terms |
law of segregation : paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors | https://openstax.org/books/concepts-biology/pages/8-key-terms |
linkage : a phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together | https://openstax.org/books/concepts-biology/pages/8-key-terms |
model system : a species or biological system used to study a specific biological phenomenon to gain understanding that will be applied to other species | https://openstax.org/books/concepts-biology/pages/8-key-terms |
monohybrid : the result of a cross between two true-breeding parents that express different traits for only one characteristic | https://openstax.org/books/concepts-biology/pages/8-key-terms |
parental generation (P) : the first generation in a cross | https://openstax.org/books/concepts-biology/pages/8-key-terms |
phenotype : the observable traits expressed by an organism | https://openstax.org/books/concepts-biology/pages/8-key-terms |
Punnett square : a visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid | https://openstax.org/books/concepts-biology/pages/8-key-terms |
recessive : describes a trait whose expression is masked by another trait when the alleles for both traits are present in an individual | https://openstax.org/books/concepts-biology/pages/8-key-terms |
reciprocal cross : a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross | https://openstax.org/books/concepts-biology/pages/8-key-terms |
recombination : the process during meiosis in which homologous chromosomes exchange linear segments of genetic material, thereby dramatically increasing genetic variation in the offspring and separating linked genes | https://openstax.org/books/concepts-biology/pages/8-key-terms |
test cross : a cross between a dominant expressing individual with an unknown genotype and a homozygous recessive individual; the offspring phenotypes indicate whether the unknown parent is heterozygous or homozygous for the dominant trait | https://openstax.org/books/concepts-biology/pages/8-key-terms |
trait : a variation in an inherited characteristic | https://openstax.org/books/concepts-biology/pages/8-key-terms |
wild type : the most commonly occurring genotype or phenotype for a given characteristic found in a population | https://openstax.org/books/concepts-biology/pages/8-key-terms |
X-linked : a gene present on the X chromosome, but not the Y chromosome | https://openstax.org/books/concepts-biology/pages/8-key-terms |
The model of the double-helix structure of DNA was proposed by Watson and Crick. The DNA molecule is a polymer of nucleotides. Each nucleotide is composed of a nitrogenous base, a five-carbon sugar (deoxyribose), and a phosphate group. There are four nitrogenous bases in DNA, two purines (adenine and guanine) and two p... | https://openstax.org/books/concepts-biology/pages/9-chapter-summary |
Prokaryotes contain a single, double-stranded circular chromosome. Eukaryotes contain double-stranded linear DNA molecules packaged into chromosomes. The DNA helix is wrapped around proteins to form nucleosomes. The protein coils are further coiled, and during mitosis and meiosis, the chromosomes become even more great... | https://openstax.org/books/concepts-biology/pages/9-chapter-summary |
DNA replicates by a semi-conservative method in which each of the two parental DNA strands act as a template for new DNA to be synthesized. After replication, each DNA has one parental or âoldâ strand, and one daughter or ânewâ strand. | https://openstax.org/books/concepts-biology/pages/9-chapter-summary |
Replication in eukaryotes starts at multiple origins of replication, while replication in prokaryotes starts from a single origin of replication. The DNA is opened with enzymes, resulting in the formation of the replication fork. Primase synthesizes an RNA primer to initiate synthesis by DNA polymerase, which can add n... | https://openstax.org/books/concepts-biology/pages/9-chapter-summary |
The ends of eukaryotic chromosomes pose a problem, as polymerase is unable to extend them without a primer. Telomerase, an enzyme with an inbuilt RNA template, extends the ends by copying the RNA template and extending one end of the chromosome. DNA polymerase can then extend the DNA using the primer. In this way, the ... | https://openstax.org/books/concepts-biology/pages/9-chapter-summary |
In prokaryotes, mRNA synthesis is initiated at a promoter sequence on the DNA template. Elongation synthesizes new mRNA. Termination liberates the mRNA and occurs by mechanisms that stall the RNA polymerase and cause it to fall off the DNA template. Newly transcribed eukaryotic mRNAs are modified with a cap and a poly-... | https://openstax.org/books/concepts-biology/pages/9-chapter-summary |
The central dogma describes the flow of genetic information in the cell from genes to mRNA to proteins. Genes are used to make mRNA by the process of transcription; mRNA is used to synthesize proteins by the process of translation. The genetic code is the correspondence between the three-nucleotide mRNA codon and an am... | https://openstax.org/books/concepts-biology/pages/9-chapter-summary |
The players in translation include the mRNA template, ribosomes, tRNAs, and various enzymatic factors. The small ribosomal subunit binds to the mRNA template. Translation begins at the initiating AUG on the mRNA. The formation of bonds occurs between sequential amino acids specified by the mRNA template according to th... | https://openstax.org/books/concepts-biology/pages/9-chapter-summary |
While all somatic cells within an organism contain the same DNA, not all cells within that organism express the same proteins. Prokaryotic organisms express the entire DNA they encode in every cell, but not necessarily all at the same time. Proteins are expressed only when they are needed. Eukaryotic organisms express ... | https://openstax.org/books/concepts-biology/pages/9-chapter-summary |
alternative RNA splicing : a post-transcriptional gene regulation mechanism in eukaryotes in which multiple protein products are produced by a single gene through alternative splicing combinations of the RNA transcript | https://openstax.org/books/concepts-biology/pages/9-key-terms |
codon : three consecutive nucleotides in mRNA that specify the addition of a specific amino acid or the release of a polypeptide chain during translation | https://openstax.org/books/concepts-biology/pages/9-key-terms |
deoxyribose : a five-carbon sugar molecule with a hydrogen atom rather than a hydroxyl group in the 2' position; the sugar component of DNA nucleotides | https://openstax.org/books/concepts-biology/pages/9-key-terms |
DNA ligase : the enzyme that catalyzes the joining of DNA fragments together | https://openstax.org/books/concepts-biology/pages/9-key-terms |
DNA polymerase : an enzyme that synthesizes a new strand of DNA complementary to a template strand | https://openstax.org/books/concepts-biology/pages/9-key-terms |
double helix : the molecular shape of DNA in which two strands of nucleotides wind around each other in a spiral shape | https://openstax.org/books/concepts-biology/pages/9-key-terms |
epigenetic : describing non-genetic regulatory factors, such as changes in modifications to histone proteins and DNA that control accessibility to genes in chromosomes | https://openstax.org/books/concepts-biology/pages/9-key-terms |
exon : a sequence present in protein-coding mRNA after completion of pre-mRNA splicing | https://openstax.org/books/concepts-biology/pages/9-key-terms |
gene expression : processes that control whether a gene is expressed | https://openstax.org/books/concepts-biology/pages/9-key-terms |
genetic code : the amino acids that correspond to three-nucleotide codons of mRNA | https://openstax.org/books/concepts-biology/pages/9-key-terms |
helicase : an enzyme that helps to open up the DNA helix during DNA replication by breaking the hydrogen bonds | https://openstax.org/books/concepts-biology/pages/9-key-terms |
intron : nonâprotein-coding intervening sequences that are spliced from mRNA during processing | https://openstax.org/books/concepts-biology/pages/9-key-terms |
lagging strand : during replication of the 3' to 5' strand, the strand that is replicated in short fragments and away from the replication fork | https://openstax.org/books/concepts-biology/pages/9-key-terms |
leading strand : the strand that is synthesized continuously in the 5' to 3' direction that is synthesized in the direction of the replication fork | https://openstax.org/books/concepts-biology/pages/9-key-terms |
mismatch repair : a form of DNA repair in which non-complementary nucleotides are recognized, excised, and replaced with correct nucleotides | https://openstax.org/books/concepts-biology/pages/9-key-terms |
mRNA : messenger RNA; a form of RNA that carries the nucleotide sequence code for a protein sequence that is translated into a polypeptide sequence | https://openstax.org/books/concepts-biology/pages/9-key-terms |
mutation : a permanent variation in the nucleotide sequence of a genome | https://openstax.org/books/concepts-biology/pages/9-key-terms |
nitrogenous base : a nitrogen-containing molecule that acts as a base; often referring to one of the purine or pyrimidine components of nucleic acids | https://openstax.org/books/concepts-biology/pages/9-key-terms |
nontemplate strand : the strand of DNA that is not used to transcribe mRNA; this strand is identical to the mRNA except that T nucleotides in the DNA are replaced by U nucleotides in the mRNA | https://openstax.org/books/concepts-biology/pages/9-key-terms |
nucleotide excision repair : a form of DNA repair in which the DNA molecule is unwound and separated in the region of the nucleotide damage, the damaged nucleotides are removed and replaced with new nucleotides using the complementary strand, and the DNA strand is resealed and allowed to rejoin its complement | https://openstax.org/books/concepts-biology/pages/9-key-terms |
Okazaki fragments : the DNA fragments that are synthesized in short stretches on the lagging strand | https://openstax.org/books/concepts-biology/pages/9-key-terms |
phosphate group : a molecular group consisting of a central phosphorus atom bound to four oxygen atoms | https://openstax.org/books/concepts-biology/pages/9-key-terms |
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