Weak forces in Evolution

1. Weak forces in Evolution Dan Graur

2. Changes in allele frequencies are important. Changes in genotype frequencies are not so important. 1. 2.

3. Mating

4. Deviation from randomness: By genetic similarity: Assortative mating Disassortative mating By genetic relatedness: Inbreeding Outbreeding

5. Skin color

6. disassortative assortative

7. Human assortative mating: Rule #1

8. Strong assortative mating by skin color in the US Percentage of non-hispanic whites: 80% Percentage of blacks: 13% Expected percentage of interracial marriages: 10.4% Observed percentage of interracial marriages: 0.9% Ratio of = 2:1 white female/black male black female/white male

9. Assortative mating is very strong in humans even with respect to non-genetic traits.

10. Degrees of inbreeding found in nature:

12. P = Ptolemy C = Cleopatra Inbreeding is usually forbidden… P ix C v P xii C vii An exception!

13. The fish Rivulus marmoratus exhibits the most extreme form of inbreeding: Selfing

14. Random mating  equilibrium allele frequencies

15. Assortative mating  excess homozygotes

16. Disassortative mating  excess heterozygotes

17. Even if extreme deviations from random mating occur in all generations, allele frequencies remain constant.

18. Mating pattern is not an important evolutionary force

19. Clinical effects of inbreeding P.T. Barnum + Tom Thumb

20. Clinical effects of inbreeding

22. Migration

24. Migration will cause changes in the allele frequencies of each of the two subpopulations.

25. However, because of gene flow, the two subpopulations are, in fact, one population, in which allele frequencies do no change.

26. Genotype frequencies will change in a similar fashion to that in disassortative mating.

27. Migration is not an important evolutionary force

28. Mutation Mutation: A transmissible change in the genetic material

29. Mutations are the ultimate source of variation. Only mutations can create genetic novelty.

30. Mutations arise all the time. Per definition, the initial frequency of a mutation in a diploid population is 1/2N.* *N = population size

31. The human population on October 31, 2011 was estimated to be 7 billion people. The number of alleles at an autosomal locus is, therefore, 14 billion. A mutation arising today in the human population will have an initial frequency of about 7 × 10-11… …resulting in a change in allele frequencies from0to0.00000000007.

33. Mutation is the ultimate source of variability, but it is not an important evolutionary force.

34. For a mutation to become significant, it must increase its frequency, so that it becomes fixed* in the population. *frequency of allele = 1.0

35. Two factors can lead to the fixation of a new mutation: Selection Random genetic drift