Datasets:
Genetics, DNA, and Heredity
The Basics
What is DNA?
It's a history book -
a narrative of the journey of our
species through time.
It's a shop manual, with an incredibly detailed blueprint
for building every human cell.
And it's a transformative textbook of medicine, with
insights that will give health care providers immense new powers to treat, prevent and cure disease."
- Francis Collins
What Does DNA Look Like?
A
G
T
C
Every cell in our body has the same DNA….
Eye cell
Karyotype
Lung cell
Toe cell
How much DNA is in one cell?
Genome = 46 chromosomes
Genome = approx. 3 billion base pairs
One base pair is 0.00000000034 meters
DNA sequence in any two people is 99.9% identical – only 0.1% is unique!
What makes one cell different from another?
DNA = “the life instructions of the cell”
Gene = segment of DNA that tells the cell how to make a certain protein.
Allele = one of two or more different versions of a gene
Sequence for normal adult hemoglobin:
Sequence for mutant hemoglobin:
Wild-type Hemoglobin Protein
Mutant Protein
Normal Red Blood Cell
Abnormal Red Blood Cell
The Human Genome Project Goals
• To sequence (i.e. determine the exact order of nucleotides (A,T,G,C) for ALL of the DNA in a human cell
• To determine which sections of DNA represent
individual genes (protein-coding units).
The HGP: International effort to decipher the blueprint of a human being.
How It Was Done
DNA samples collected from thousands of volunteers
Samples sent to Human Genome Project centers across the world
Scientists at centers perform DNA sequencing and analysis
• February 2001: Draft of the
sequence published in Nature (public effort )and Science (Celera – private company).
• April, 2003 (50 years after
Watson and Crick structure of DNA was published) : Full sequence published and researchers determined that within this sequence there was somewhere between 30,000 and 40,000 genes. We now believe there are closer to 25,000 genes
Still A Lot of Work To Do . . .
Comparing the genomes of humans and other organisms
Discovering DNA and gene functions
Investigating interactions between DNA sequences, gene products, and environmental factors
Analyzing genetic variation between individuals and populations
How Can We Use This Information?
Better understanding of human disease
Personalized medicine & Pharmacogenetics
Greater insight into cognitive function
Insight into human origins
Identifying genetic susceptibility to disease
Inheritance of Genes
Gregor Mendel
1822-1884
• Augustinian monk who
cross-bred pea plants with different characteristics • Observations led to laws
regarding the transmission of hereditary characteristics from generation to generation • Many of the concepts from his observations still hold true today!
Picture from www.nih.nlm.gov
Mendel’s Laws:
- Principle of Segregation: Two members of a
gene pair segregate from each other in the formation of gametes; half the gametes carry one allele, and the other half carry the other allele What it means: each gene has two copies (alleles) and a parent will give only one copy to a child. The other parent will give another copy, and thus the child will receive two copies (alleles) – one from each parent. Each child will literally be half-mom and half-dad!
Mendel’s Laws:
- Principle of Independent Assortment:
Genes for different traits assort independently of one another in gamete production What it means: different genes are inherited separately. For example, the gene which codes for eye color is inherited separately from the gene which codes for nose shape.
Mendelian Concepts
Dominant = only one allele of a gene necessary to express the trait Recessive = both alleles of a gene must be identical to express the trait Heterozygous = alleles of a particular gene are non-identical Homozygous = alleles of a particular gene are identical
Applying Mendelian Concepts: The Punnett Square
Parent 2
Allele 1
Allele 2
Allele 1
A1/A1 A1/A2
Parent 1
Allele 2
A2/A1 A2/A2
Homozygous dominant + Homozygous dominant
Homozygous dominant + Heterozygous
A
A
A
A
A
AA
AA
A
AA
AA
A
AA
AA
a
Aa
Aa
Homozygous dominant + Homozygous recessive
a
a
A
Aa
Aa
A
Aa
Aa
Heterozygous + Heterozygous
A
a
AA
Aa
Aa
aa
A
a
EXAMPLE
• Dan and Kim are going to have a baby. Kim has dimples in her cheeks (a dominant trait), while Dan does not.
• What are the chances Dan and Kim’s baby will have dimples?
We know Dan and Kim’s phenotypes (no dimples/dimples), but what are their genotypes?
• Dan has the recessive trait (no dimples)
– He must have two recessive alleles – Dan’s genotype can be represented as ‘dd’
• Kim has the dominant trait (dimples)
– But Kim could be homozygous dominant OR
heterozygous dominant
– Kim’s genotype can be either ‘DD’ or ‘Dd’ – Which one is it?
More information
• What if you knew something about Kim’s
parents?
• How could that help?
Kim’s Parents
• As it turns out, Kim’s father has dimples in both cheeks, while her mother does not • Her mother must have the recessive trait and therefore has to have the genotype ‘dd’
• Kim’s father has the dominant trait, but we
don’t know if he is a homozygote or heterozygote. He could be ‘DD’ or ‘Dd’ just like Kim!
• But we still know what Kim’s genotype
must be. Why?
Kim’s genotype is ‘Dd’
• Kim must have a recessive allele (d), since that is all she could have inherited from her mother
• Since Kim has dimples, we know she
inherited a dominant allele (D) from her father – It doesn’t matter if Kim’s father is DD or Dd; whichever it is, he passed on a ‘D’ to his daughter
What are the chances Kim and Dan’s baby will have dimples?
Kim
d
D
Dan
d
d
Kim
d
D
Dd
dd
Dd
dd
Dan
d
d
50% chance the baby will have the genotype ‘Dd’ and have dimples
50% chance the baby will have the genotype ‘dd’ and not have dimples
Clinical Application
P
Clinical Application continued . . .
P
Other things may change us, but we start and end with family
-Anthony Brandt
If you look deeply into the palm of your hand, you will see your parents and all generations of your ancestors. All of them are alive in this moment. Each is present in your body. You are the continuation of each of these people.
-Thich
Nhat
Hanh
Questions?
Adapted from a Presentation Created by the University of North Carolina DNA Day Program
• Sponsors
– NC Glaxo Smith Kline Foundation – National Human Genome Research Institute – Sigma XI Scientific Research Society
• Collaborative Partners
– North Carolina Department of Public Instruction – Destiny Traveling Science Learning Program – North Carolina Association for Biomedical Research – National Human Genome Research Institute – American Society for Human Genetics
• North Carolina Educators
– Amy Bradley, Hibriten High School; Cindy Byron, School of Inquiry and Life Sciences at Asheville (SILSA); Anita Crowley, Lee County High School; MaryAnne Gore, West Brunswick High School; Terry Howerton, The School of Biotechnology at Atkins; Michael Kendall, East Bladen High School; Crystal McDowell; Letitia Myles, E.E. Smith High School; Elizabeth Pressley, Bartlett Yancey High School; Steven Ross, Harnett Central High School; Murphey Wellman, North Iredell High School; Anita Willington, East Bladen High School; Linda Woody, Reidsville High School