1. 1 BSCI 363: read the rest of chapter 9 CONS 670: read the rest of chapter 7, and chapter 9

2. 2 stabilizingdirectional disruptive As natural selection begins After selection has occurred 26 P decreases H depends on genotype favored by selection

3. 3 stabilizingdirectional disruptive As natural selection begins After selection has occurred 26 PHPH PHPH PHPH ?? ?

4. 4 Dynamic Effects: Natural Selection maintains allele frequencies in equilibrium with environmental demands vs. Genetic Drift pulls allele frequencies away from environmental equilibrium 31a-2

5. 5 5 causes of microevolution 1) genetic drift - stochastic variation in inheritance 2) Assortative mating 3) Mutation 4) Natural selection 5) Migration (gene flow) 31a-2

6. 6 E migration / I mmigration Donor populationRecipient population Pollen grains emigration from one population and immigration into the other; breeding = Gene flow Migration (m) of breeding individuals results in increased H and increased P 41f4

7. 7 Models of gene flow based on population structure metapopulation subpopulation 1. Continent to island modele.g., Madagascar (source - sink model) 2. Equivalent island model e.g., Philippines 30-1

8. 8 3. Stepping-stone modele.g., Hawaiian Islands 4. Isolation by distance model (continuous habitat) e.g., Amazon forest Genetic neighborhood 30-2

9. 9 Gene flow results in homogenization of allele frequencies on “islands” of equivalent size. * * assume thorough gene flow between populations 30e Before gene flow: After: A =.7 A =.6 A =.5 A =.4 A =.55.7.6.5.4 X =.55 m

10. 10 Changes in allele frequency due to migration m ij = gene flow = # breeding immigrants from donor population j size of recipient population i migrants (m) moving from donor (j) to recipient (i) Change in allele frequency (q) in population i: BeforeAfter Recipient i q i q i ’ = (1-m ij ) q i + m ij q j Donor j q j q j j i “jump”“into” 41A

11. 11 Gene flow example BeforeN e = 200 N e = 300 q j = 0.9 q i = 0.5 Afterq j ’ = 0.9 q i ’ = 0.51 m ij = 5 = 0.0167 300 q i’ = (1 - m ij ) q i + m ij (q j ) = (1 - 0.0167) (.5) + (0.0167) (0.9) = (0.5067) = 0.51 (If number of immigrants = 50, then q i’ = 0.57) Donor population (j) Recipient (i) 41e 5 individuals

12. 12 Gene flow: major points 1) High m ij homogenizes allele frequencies in two populations 2) Rate of gene flow influences N e of recipient population and metapopulation 3) A small amount of gene flow may counteract genetic drift and conserve genetic diversity in small populations 4) Allele frequency in the donor population is assumed to be unchanged after gene flow to recipient population 5) Size of donor population does not influence allele frequencies in recipient populations 6) Applications: calculate number of individuals needed to introduce into recipient population of known size to maintain its genetic diversity. 41f1

13. 13 Directional selection in peppered moths (Biston betularia) in England 2 phenotypes: black moth, mottle white moth Prior to 1600 (Industrial revolution) black form approximately 1% white form approximately 99% After 1600 (widespread industrial pollution, smoke and soot) black form approximately 90% white form approximately 10% Now (local pollution from smokestacks) Near pollution sourceAway black form 50% 10% white form 50% 90% Outbreeding depression? 41

14. 14 Selection and gene flow: colonization along an environmental gradient 42 Cold-adapted favored Warm-adapted favored m m m m m

15. 15 Effect of inbreeding on H Selfing: In a population with f (a) = f (A) = 0.5 At Hardy-Weinberg equilibrium, genotypic frequencies are p 2 + 2pq + q 2 = 1 AA Aa aa Parental genotypic frequencies:.25.50.25 F 1 homozygotes.25.25 F 1 heterozygotes.125.25.125 F 1 genotypes.375.25.375 Conclusion: Frequency of heterozygotes is reduced by 50% with each generation of selfing. But there is no loss of allelic diversity: f (a) = f (A) = 0.5 43

16. 16 (1-s) H S = ---------------2pq (1- s/2) H S = equilibrium heterozygote frequency (random + selfing) s = proportion of selfing The case of selfing with some random mating too The frequency of heterozygotes will always fall between 2pq and 0 44?

17. 17.5 0.1.2.3.4 HtHt Time in generations 0 20 Brother-sister (sibs) Selfing 45-1 The loss of heterozygosity through time caused by inbreeding

18. 18 Generations 52143 Loss of H t 0.75 0.50 0.25 Full-sibs Half-sibs Double first cousins First cousins 45-2

19. 19 Genetic consequences of inbreeding 1) decrease in heterozygosity, no change in P (allelic diversity) (the more related the individuals, the faster the loss of H) 2) increases the probability of a zygote receiving identical alleles (homologous alleles), which will result in increased expression of recessive alleles. 3) increased phenotypic expression of deleterious alleles (strongly selected against) - often results in decreased size, reproduction, vigor, etc., which decrease fitness (i.e., inbreeding depression) 4) increase in phenotypic variability resulting from a deviation from the mean genotypes in non-inbred individuals 43e-1 Genetic load

20. 20 Inbreeding coefficient Sewall Wright (1923) F = the probability that an individual will receive two equal alleles, at a specific locus, that are from the same ancestor. Autozygous = identical by descent allozygous = not identical by descent F = probability that an individual will be autozygous at a given locus 1 - F = probability that an individual will be allozygous at a given locus 43e-2

21. 21 Calculate Junior’s inbreeding coefficients from this pedigree: AB CD MomDad AC CC C =.5 Sis Junior (or could be DD from Dad) Probability of C from Dad to Sis to Junior =.25 Probability of C from Dad to Junior =.50 Probability of Jr. inheriting CC from Dad =.25 X.50 =.125 Probability of Junior inheriting DD from Dad =.125 F =.125 +.125 =.25= probability of Jr. being autozygous 31