1. Measuring Evolution within Populations

2. 5 agents of evolutionary change
Mutation
Gene Flow
Non-random mating
Genetic Drift
Selection
Chemical Changes to DNA
Migration
Sexual Selection
Natural Selection Differential Survival
Small population

3. Hardy-Weinberg Equilibrium
Hypothetical situation
Serves as a null hypothesis
A non-evolving population
Remove all agents of evolutionary change
1. No genetic drift (a very large population)
2. No gene flow (no migration in or out)
3. No mutation (no chemical change to DNA)
4. Random mating (no sexual selection)
5. No natural selection (equal survival)

4. Hardy-Weinberg Equations
If the previous conditions are met, then …
p2 + 2pq + q2 = 1
p + q = 1
p = frequency of dominant allele (B)
q = frequency of recessive allele (b)
p2 = % of homozygous dominant individuals (BB)
q2 = % of homozygous recessive individuals (bb)
2pq = % of heterozygous individuals (Bb)

5. Hardy-Weinberg Equations
p2 + 2pq + q2 = 1
p + q = 1
Cystic fibrosis is a recessive condition (cc) that affects 1 in 2,500 babies in the Caucasion population in the U.S.
What is the frequency of the recessive allele?
q2 = 1/2500 =
q = √ = 0.02 (or 2%)

6. Hardy-Weinberg Equations
p2 + 2pq + q2 = 1
p + q = 1
Cystic fibrosis is a recessive condition (cc) that affects 1 in 2,500 babies in the Caucasion population in the U.S.
What is the frequency of the dominant allele?
p = 1 - q
p = = .98 (or 98%)

7. Hardy-Weinberg Equations
p2 + 2pq + q2 = 1
p + q = 1
Cystic fibrosis is a recessive condition (cc) that affects 1 in 2,500 babies in the Caucasion population in the U.S.
What is the percentage of heterozygotes in the population?
2pq = 2(.98)(.02) = (or 4% … or 1 in 25)

8. Example of strong selective pressure
Tay Sachs
Primarily in Ashkenazi Jews and Cajuns
Recessive disease = aa
Lysosomal storage disease
Lack of 1 functional digestive enzyme in lysosome
Build up undigested fat in brain cells
Children die before the age of 5
So where do new cases of Tay-Sachs come from?

9. Example of heterozygote advanage
Sickle Cell Anemia
Inherit a mutation in gene coding for one of the subunits in hemoglobin
Oxygen-carrying blood protein
Normal allele = Hb
Sickle allele = Hs
Recessive trait = HsHs
Low oxygen levels cause RBC to sickle
Clogs small blood vessels
Damages organs
Often lethal

10. Suggests some selective advantage of being heterozygous… HbHs
Sickle Cell Frequency
High frequency of heterozygotes
1 in 5 in Central Africans = HbHs
Unusual for individuals with homozygous recessive genotype
1 in 100 = HsHs
Usually die before reproductive age
Why is the Hs allele maintained at such high levels in African populations?
Suggests some selective advantage of being heterozygous… HbHs

11. Malaria
Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells 1
liver 2 3

12. Heterozygote advantage
In tropical Africa where malaria is common:
Homozygous dominant (normal)
Reduced survival or reproduction due to malaria (HbHb)
Homozygous recessive
Reduced survival or reproduction due to sickle cell disease (HsHs)
Heterozygote carriers
Survival & reproductive advantage (HbHs)