1. Measuring Evolution of Populations

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

3. Hardy-Weinberg equilibrium
Hypothetical situation
serves as null hypothesis
non-evolving population
REMOVE all agents of evolutionary change
no genetic drift (very large population size )
no gene flow (no migration in or out)
no mutation (no chemical change to DNA)
random mating (no sexual selection)
no natural selection (equal survival)

4. The Hardy-Weinberg Formula
The Hardy-Weinberg formula can be used to determine if a population is in genetic equilibrium
p2(AA) + 2pq (Aa) +q2(aa) = 1.0
The frequency of the dominant allele (A) plus the recessive allele (a) equals 1.0
p + q = 1.0

5. A Population in Equilibrium

6. If 98 out of 200 individuals in a population express the recessive phenotype, what percent of the population would you predict would be heterozygotes?
Q2 = 98/200 = .49 q = square root .49 = .7 p = .3 (p + q = 1 so p + .7 = 1) 2pq = 2 x .7 x .3 = .42 = 42%

7. Directional Selection
Changing environmental conditions can shift allele frequencies in a consistent direction
Forms of traits at one end of a range of phenotypic variation become more common

8. Predation and Rock-Pocket Mice
In rock-pocket mice, two alleles of a single gene control coat color
Night-flying owls are the selective pressure that directionally shifts the allele frequency

9. Stabilizing Selection: Body Weight of Sociable Weavers
Natural selection that favors an intermediate phenotype and eliminates extreme forms

10. Disruptive Selection Disruptive selection
Natural selection that favors extreme forms of a trait and eliminates the intermediate forms

11. Example of strong selection pressure
Tay Sachs
primarily in Ashkenazi Jews & Cajuns
recessive disease = aa
lysosomal storage disease
lack of one functional digestive enzyme in lysosome
build up undigested fat in brain cells
children die before they are 5 years old
So where do new cases of Tay-Sachs come from?

12. Sexual Selection
Sexual selection acts on an organism's ability to obtain or successfully copulate with a mate
Sexual selection is often powerful enough to produce features that are harmful to the individual's survival.
Peacock Video - 11 minutes

13. Example of heterozygote advantage
Sickle cell anemia
inherit a mutation in gene coding for one of the subunits in hemoglobin
oxygen-carrying blood protein
normal allele = Hb
mutant allele = Hs
recessive trait = HsHs
low oxygen levels causes RBC to sickle
clogging small blood vessels
damage to organs
often lethal

14. Sickle cell frequency High frequency of heterozygotes
1 in 5 in Central Africans = HbHs
unusual for allele with severe detrimental effects in homozygotes
1 in 100 = HsHs
usually die before reproductive age
Sickle Cell:
In tropical Africa, where malaria is common, the sickle-cell allele is both an advantage & disadvantage. Reduces infection by malaria parasite.
Cystic fibrosis:
Cystic fibrosis carriers are thought to be more resistant to cholera:
1:25, or 4% of Caucasians are carriers Cc
Why is the Hs allele maintained at such high levels in African populations?
Suggests some selective advantage of being heterozygous… HbHs

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

16. Heterozygote Advantage
In tropical Africa, where malaria is common:
homozygous dominant (normal)
reduced survival or reproduction from malaria: HbHb
homozygous recessive
reduced survival & reproduction from sickle cell anemia: HsHs
heterozygote carriers
survival & reproductive advantage: HbHs
Hypothesis:
In malaria-infected cells, the O2 level is lowered enough to cause sickling which kills the cell & destroys the parasite.
Frequency of sickle cell allele & distribution of malaria