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1. 2: Population genetics break

2. Two subpopulations A: p=0 A: p=1 a: q=1 a: q=0 In such a case, there are no heterozygous individuals in the population, although according to HW, there should be. There is a deficit in heterozygous. Is this phenomenon general?

3. Two subpopulations Subpopulation 1 Subpopulation 2 A: p2 A: p1 a: q2 a: q1 We assume panmixia (random mating) in each subpopulation.

4. Two subpopulations Subpopulation 1 Subpopulation 2 A: p2 A: p1 a: q2 a: q1 We assume N1 individuals in population 1, N2 individuals in population 2. Let N=N1+N2. Let K1 be the fraction of population 1 out of the entire population: K1 = N1/N. K2 = 1-K1.

5. Two subpopulations Subpopulation 1 Subpopulation 2 A: p2 A: p1 a: q2 a: q1 What is the general heterozygosity in subpopulation 1? This is also the HW heterozygosity, which is expected since the subpopulation is in panmixia

6. Two subpopulations Subpopulation 1 Subpopulation 2 A: p2 A: p1 a: q2 a: q1 What is the expected heterozygosity, under HW in the entire population? To compute this we first have to compute the frequency of A and a in the entire population. Then:

7. Two subpopulations The frequency of allele A in the entire population is:

8. Two subpopulations The expected heterozigosity under HW is often also called Hexp

9. Two subpopulations Hexp is the probability to sample a heterozygous if one first mix all the alleles of the entire population. The question is what is the different between this expectation and the actual frequency of heterozygous in a sample from the population.

10. Two subpopulations Hexp is the probability to sample a heterozygous if one first mix all the alleles of the entire population. The question is what is the different between this expectation and the actual frequency of heterozygous in a sample from the population.

11. Two subpopulations A: p1 A: p2 a: q2 a: q1 K 1-K Probability to sample subpopulation 1 Probability to sample a heterozygous individual in subpopulation 1

12. Two subpopulations A: p1 A: p2 a: q2 a: q1 K 1-K We will show that Hobs is always smaller than Hexp and that this is a general phenomenon for subpopulations.

13. Heterozygote deficit F= (Hexp-Hobs)/Hexp Heterozygote deficit (also known as Inbreeding coefficient) F measures the fractional reduction in heterozygosity relative to random mating

14. Rewriting F

15. Rewriting F

16. Simplifying terms F is always non negative -> reduction in heterozygosity relative to random mating is a general phenomenon when there is non random mating.

17. Heterozygote deficit A: p1 A: p2 a: q2 a: q1 K 1-K F>0 we have a heterozygote deficit F=0 when p1=p2 (or K=0). F varies depending on the locus considered

18. Heterozygote deficit p2 p4 p1 p3 Pn … The above argument for two subpopulations also holds true for more than two subpopulations…

19. Wahlund effect This reduction is called the Wahlund effect

20. 2: Population genetics break

21. Other mechanisms that can cause a heterozygote deficit in a population Non random mating (no panmixia): 1. Autogamy = autofecondation 2. Positive assortative mating = sexually reproducing organisms that tend to mate with individuals that are like themselves in some respect.

22. Autogamy: Cleistogamy flowers Cleistogamy = the character “closed flowers”, which is directly linked to self-pollination. All the genes in the individual will slowly loose genetic diversity.

23. Positive assortative mating Animals that choose partners with a specific character as they have (e.g., a fly with red eye will prefer to mate with a fly with red eye). Not all the genes will loose genetic diversity to the same extent. The genes responsible for the selected type of segregation will be most homozygous.

24. Excess of heterozygote Negative assortative mating = sexually reproducing organisms tend to mate with individuals that are different from themselves in some respect. Advantage of the rare = individual with rare genotypes will reproduce more.

25. Negative assortative mating: an example The Sporophytic (the diploid form of plants) Self-Incompatibility (SSI) The female part of a plant

26. Advantage of the rare • In some mating systems a male bearing a rare allele will have a mating advantage. Rare allele advantage will tend to increase the frequency of the rare allele and hence increase heterozygosity. This is also true for the human population.