Chpt. 23 The Evolution of Populations-- Population Genetics

1. Chpt. 23 The Evolution of Populations-- Population Genetics

2. Individuals are selected… Populations evolve

3. Individuals are selected… Populations evolve

4. Populations = unit of evolution Natural selection = mechanism of evolution Gradualism= accumulation of small changes in gene pool over LONG periods of time

5. Hardy-WeinbergTheorem

6. Hardy-WeinbergTheorem • examines the gene structure of a NON-evolvingpopulation

7. Hardy-WeinbergTheoremexamines the gene structure of a NON-evolving population. • Obviously, this is not common, however, gives a base-line / modelNULL HYPOTHESIS for determining if and why populations evolve

8. Hardy-WeinbergTheoremeven though alleles are shuffled and recombined during meiosis and random fertilization. This has no effect on the overall gene pool percentages.

9. A a a a A A a A A a A a A Not SWIMMING pool…. a GENE POOL!!!

10. Hardy-WeinbergTheorem Gene pool frequencies (percentages) will remainunchanged if nomechanismthatcancauseevolutiontooccuractsonapopulation.

11. Hardy-WeinbergTheorem Gene pool frequencies will remain unchanged if: Mutations are not occurring

12. Hardy-WeinbergTheorem Gene pool frequencies will remain unchanged if: Natural selection is not occurring

13. Hardy-WeinbergTheorem Gene pool frequencies will remain unchanged if: Population is LARGE

14. Hardy-WeinbergTheorem Gene pool frequencies will remain unchanged if: EVERYONE breeds…

15. Hardy-WeinbergTheorem Gene pool frequencies will remain unchanged if: EVERYONE randomly mates…

16. Hardy-WeinbergTheorem Gene pool frequencies will remain unchanged if: EVERYONE produces the same number of offspring

17. Hardy-WeinbergTheorem Gene pool frequencies will remain unchanged if: NOONE migrates in or out of the population… everyone stays

18. Hardy-WeinbergTheorem Yeah, right.... when does THAT happen?

19. 5 Agents of evolutionary change: Mutation Gene Flow (migration) Non-random mating Selection Genetic Drift (same # of offspring)

20. Hardy-WeinbergTheoremremember:H.W. explains: the frequencyof allelesremainsconstant in a population… unless acted upon by agents OTHER THAN sexual recombination.

21. Hardy-Weinberg Principle Mathematical statement about the relative frequency of alleles (genotypes) in a population. p +q = 1 p2 + 2pq + q2 = 1

22. Hardy-WeinbergTheorem • Frequency of alleles remainsconstant in a population, unless acted upon by agents OTHER THAN sexual recombination. • Inheritancedoesnotcausechangesinallelefrequency. Remember:

23. Hardy-Weinberg Principle p = frequency of dominant allele p + q = 1

24. Hardy-Weinberg Principle q = frequency of recessive allele p + q = 1

25. Hardy-Weinberg Principle Mathematical statement about the relative frequency of alleles (genotypes) in a population. in most cases, we only know the phenotypic frequencies

26. Hardy-Weinberg Principle q2 = frequency of homozygoterecessiveindividuals q2 = # of aa individuals

27. Hardy-Weinberg Principle p2 = frequency of homozygotedominantindividuals p2 = # of AA individuals

28. Hardy-Weinberg Principle p = frequency of dominantallele p = # of (AA) + 2 (# Aa)

29. Hardy-Weinberg Principle q = frequency of recessiveallele q = # of (aa) + 2 (# Aa)

30. Hardy-Weinberg Principle 2pq = frequency of heterozygoteindividuals 2pq= # of Aa individuals

31. Hardy-Weinberg Principle by comparing genotypic frequencies from one generation to the next, you can learn whetherornot evolution has occurred…

32. Hardy-Weinberg Principle if genotypic frequencies have changed from your original count… evolution has occurred!

33. Suppose there are 1,000 individuals in a population Genotype NumberGenotypicFrequency AA 490 0.49 Aa 420 0.42 aa 90 0.09 total 1000 1.00

34. Suppose there are 1,000 individuals in a population GenotypicFrequency Genotypic frequency = the proportion of a particular genotype found in a population 0.49 0.42 0.09 total 1.00 AA Aa aa

35. Suppose there are 1,000 individuals in a population Phenotype NumberPhenotypicFrequency dominant 910 0.91 recessive 90 0.09 total 1000 1.00

36. Suppose there are 1,000 individuals in a population PhenotypicFrequency Phenotypic frequency = the proportion of a particular phenotype found in a population 0.91 0.09 total 1.00

37. Suppose there are 1,000 individuals in a population Allele NumberAlleleFrequency A 1400 0.7 a 420 0.3 total 2000 1.00

38. q = frequency of recessive allele However, we do not know how many a’s there are just by looking at phenotype 480 Allele frequency Pssst…(There are 1,000 copies of the flower color gene in this population of 500 total flowers…) q =

39. q2 = frequency of recessive genotype 480 Genotypic frequency q2 = 20/500

40. q2 = frequency of recessive genotype 480 Genotypic frequency q2 = .04

41. q = frequency of recessive allele 480 Allele frequency q = .04

42. q = frequency of recessive allele 480 Allele frequency q = .2

43. q = frequency of recessive allele p = frequency of dominant allele 480 q = .2 Allele frequency p + q = 1 p + .2 = 1 p = 1 - .2 p = .8

44. 480 p = .8 q = .2 Some of the pink flowers will be AA and some will be Aa p2 + 2pq + q2 = 1

45. 480 Some of the pink flowers will be AA and some will be Aa .64 + .32 + .04 = 1

46. 480 How many of the pink flowers will be AA and how many will be Aa .64 X 500 individuals 320 individuals are AA

47. 480 How many of the pink flowers will be AA and how many will be Aa .32 X 500 individuals 160 individuals are Aa

48. 480 320 are AA 160 are Aa 480 total

49. .8 x .8 = .64 Genetic structure of next generation

50. .2 x .2 = .04 Genetic structure of next generation