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Evolution

Evolution. Genetic variation. There can be no evolution without variation Mutations are the ultimate source of new variation in DNA Germ-line mutations are important for evolution. Genetic variation in natural populations. Natural populations exhibit great variation.

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Evolution

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  1. Evolution

  2. Genetic variation There can be no evolution without variation Mutations are the ultimate source of new variation in DNA Germ-line mutations are important for evolution

  3. Genetic variation in natural populations Natural populations exhibit great variation. Heterozygosity is approximately 10% for all loci.

  4. Maintaining genetic variation Adaptive genetic diversity Balanced between origin of variation by mutation and the loss by selection Neutral genetic diversity Balance between origin of variation by mutation and loss by drift

  5. Overdominance Selection favoring overdominance • favors heterozygotes • results in stable gene frequencies fitness SS SA AA

  6. Overdominance: Sickle Cell Anemia

  7. Overdominance: Sickle Cell Anemia SS = sickle-cell anemia SA = malaria resistance AA = Malaria susceptability

  8. Sickle-cell anemia

  9. Balancing Selection Case in which natural selection maintains genetic variation at frequencies above levels of mutation. …in this case, balancing selection makes the population as a whole more resistant to malaria

  10. Prion disease in Fore Tribespeople Kuru (prion disease related to Mad Cow disease) resulted from cannibalism Only heterozygotes for the Prion Protein Gene (PRNP) are resistant

  11. Underdominance Underdominance • heterozygotes have a lower fitness • results in an unstable equilibrium • Uncommon and few natural examples fitness SS SA AA

  12. Other forms of selection….

  13. Frequency-dependent selection

  14. male andromorph gynomorph

  15. andromorph

  16. Rare male effect Rare male effect (negative frequency dependent mating success)

  17. Stabilizing Selection Selection that eliminates the extremes of a distribution and favors the centre

  18. Stabilizing Selection Stabilizing selection is common in quantitative traits.

  19. Disruptive Selection Selection that favors the extremes and eliminates the middle of a frequency distribution of trait values

  20. Dull yearlings allowed to nest on territory Bright yearlings can hold their own

  21. Disruptive Selection Selection that favors the extremes and eliminates the middle of a frequency distribution of trait values

  22. Expression of variation

  23. Expression of variation

  24. Feather modification

  25. Feather modification

  26. Environmentally-induced phenotypic responses Induced response: One genotype produces multiple phenotypes

  27. Environmentally induced response Daphnia can produce helmets and spines if predators are present

  28. Other responses Barnacles will change shape of growth if a predator snail present Snails change offspring number, shell size, shell organic content in utero in presence of crayfish

  29. And Matt’s favorite….

  30. Phenotypes and reaction norms GENOTYPE PHENOTYPE

  31. Phenotypes and reaction norms GENOTYPE PHENOTYPE X ENVIRONMENT

  32. Phenotypes and reaction norms GENOTYPE PHENOTYPE X ENVIRONMENT

  33. No genetic variation underlying number of digits, so no sensitivity to population density Fecundity is much more sensitive to fecundity, and some genotypes more than others

  34. So, is phenotypic plasticity adaptive?

  35. The reaction norms themselves can be subject to selection Selection to increase sensitivity to population density would lead to the increase in frequency of G1 Selection to decrease sensitivity to density would increase the frequency of G3

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