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Mendelian Genetics in Populations II: Migration, Genetic Drift, and Nonrandom Mating

Mendelian Genetics in Populations II: Migration, Genetic Drift, and Nonrandom Mating. Motivation What happens when we depart from HW assumptions? Pattern of genetic diversity, fitness consequences. II. Migration. Also among islands, or between populations on the mainland, etc.

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Mendelian Genetics in Populations II: Migration, Genetic Drift, and Nonrandom Mating

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  1. Mendelian Genetics in Populations II: Migration, Genetic Drift, and Nonrandom Mating • Motivation • What happens when we depart from HW assumptions? • Pattern of genetic diversity, fitness consequences.

  2. II. Migration Also among islands, or between populations on the mainland, etc.

  3. Effect of migration on allele frequencies: m, 1-m, p and pm p’ = p after migration p’ = p(1-m) + pm(m) Change in p = p’ – p = p(1-m) + pm(m) – p = = p – pm + pm(m) – p = m(pm – p) Effect is to homogenize!

  4. Variation in allele frequencies among populations of red bladder campion Silene dioica

  5. Silene dioica on Skeppsvik Archipelago, Sweden

  6. Fst = (He – Ho)/ He

  7. Migration and selection in banded water snakes

  8. Banded (A1A1, A1A2 ) is dominant to unbanded (A2A2)

  9. Variation in color pattern within and between populations A = Unbanded, D = Banded, B and C = Intermediate

  10. The combined effects of selection and migration on allele frequencies in island water snakes

  11. III. Drift and Consequences for Genetic Diversity

  12. Coin Toss

  13. The founder effect in an island-hopping bird (a) A silvereye, Zosterops lateralis.

  14. Silvereyes have been documented to colonize new islands in recent history.

  15. Allelic diversity has declined along the silvereye's route of travel

  16. Simulations of genetic drift in populations of different sizes

  17. Effect of sampling variation after many generations Change in allele frequencey of Drosophila melanogaster populations

  18. Effective population size: The size of the population that would give rise to the observed loss of heterozygosity each generation, or increase of variation between populations each generation. Variation in sex ratios: Ne = (4NmNf)/(Nm + Nf) (Genghis Kahn example) Ne = harmonic mean number of individuals: example Heterozygosity decreases by 1/2Ne per generation

  19. Consequences of Fragmentation Wahlund Effect: All of the same consequences as Drift decreases heterozygosity within populations increases homozygosity within populations increases genetic relatedness within populations

  20. Population size and genetic diversity

  21. Drift and Rates of Evolutionary Change

  22. Clock like substitution rate Drift??

  23. Why are substitution rates uniform across species with different generation times??

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