Response to selection can be fast!

1. Response to selection can be fast! Selection is strong Favored allele is partially dominant Both alleles are common

3. Selection is not always “Directional” • Heterozygote advantage • Frequency dependence • Selection varying in space or time

4. Fitness A A A a a a Heterozygote advantage

5. Relative fitness of hemoglobin genotypes in Yorubans Equilibrium frequencies: peq = s/(s+t) = 0.86/(0.12+0.86) = 0.88 qeq = t/(s+t) = 0.12/(0.12+0.86) = 0.12 Predict the genotype frequencies (at birth): HW proportions 0.774 0.211 0.0144

6. Variable selection: genotypes have different fitness effects in different environments Fitness

7. Frequency-dependent selection

8. Selection Whether directional or stabilizing, causes adaptive changes in allele frequencies

9. Forces causing evolution:Random Genetic Drift Changes in allele frequency due to random sampling: not adaptive

10. 10 Populations, N=15

11. Drift occurs even in large populations!N=10,000

12. Genetic drift eliminates genetic variation

13. Forces that cause evolution Mutation Ultimate source of all genetic variation Mutation is generally not adaptive

14. How common is mutation? Achondroplastic dwarfism • Dominant autosomal allele • Recurrent mutation rate: 3/200,000 = 0.000015 per generation • q0=0.0; q1 = 0.000015, q2 = 0.000030

15. Mutation/Selection Balance Even highly deleterious mutations can persist at substantial frequency, especially if they are recessive: Selection against a recessive allele is s Genotype AA Aa aa Fitness 1 1 1-s For recessive lethal, s = 1

16. Mutation-selection equilibrium Recessive deleterious alleles: qe = √(/s) If a recessive lethal (s=1) has a recurrent mutation rate of 1.5*10-5, what is it’s equilibrium frequency? qe = 0.004

17. Mutation maintains substantial genetic variation Deleterious mutations Organismper genome/gener’n C. Elegans 0.04 D. melanogaster 0.14 Mouse 0.9 Human 1.6 HIV virus is thought to have mutation rate ~10 X greater than humans!

18. Forces causing evolution:Non-random mating:Inbreeding Mating between relatives

19. What happens to genotype frequencies under inbreeding? Most extreme form of inbreeding is selfing P: Aa x Aa F1: 25% AA 50% Aa 25% aa F2: 37.5% AA 25% Aa 37.5% aa F3: 43.75% AA 12.5% Aa 43.75% aa Fewer heterozygotes and more homozygotes each generation

20. What happens to heterozygosity under inbreeding? Generations Heterozygosity: of selfingProp. of heterozygotes 0 100% Aa 1 50% Aa 2 25% Aa 3 12.5% Aa

21. What happens to allele frequencies under inbreeding? P: Aa x Aa F1: 25% AA 50% Aa 25% aa F2: 37.5% AA 25% Aa 37.5% aa F3: 43.75% AA 12.5% Aa 43.75% aa Allele frequencies do not change under inbreeding, but population is perturbed from H-W proportions.

22. Inbreeding Depression Yield Inbreeding Coefficient

23. Pup survival relative to Inbreeding Inbreeding Coefficient Survival < 0.19 75% 0.25-0.67 51% > 0.67 25% Brother-sister or parent-offspring mating reduces the heterozygosity by 25% per generation: G0: H=1 G1: H= ? G2: H= ?

24. Proportions of individuals w/ genetic disease who are products of first cousin marriages

25. Migration between subpopulations Tends to equalize allele frequencies among subpopulations, even if the allele frequencies differ because of differing selection pressure

26. Migration: island model Migration rate= m=0.05 qm = 0.9 q = 0.1 q' = (1-m)q + mqm = q - m(q - qm) q' = 0.1 +0.04 = 0.14

27. Evolution is the result of violating assumptions of H-W • These ideas are straightforward. • Mathematics can be complicated, especially when multiple evolutionary forces are occurring simultaneously

28. Practical Considerations • Evolution of pathogens (HIV, SARS, West Nile Virus, etc.) • Evolution of antibiotic resistance • Evolution of pesticide and herbicide resistance • Conservation of genetic diversity in natural, captive, and agricultural species.