Chapter 23: The Evolution of Populations

1. Chapter 23:The Evolution of Populations

2. Population Genetics • microevolution – change in genetic makeup of a population from generation to generation

3. macroevolution – evolutionary change above the species level

4. population – group of individuals of the same species living in the same area

5. gene pool – all the genes in a given population at a given time

6. allele frequency – proportion of an allele in a gene pool • p = dominant allele • q = recessive allele f (p) = frequency of the dominant allele f (q) = frequency of the recessive allele

8. Calculating allele frequency:

10. Hardy-Weinberg Theorem • helps measure changes in allele frequencies over time • provides an “ideal” population to use as a basis of comparison

11. Conditions for Hardy-Weinberg Equilibrium: • Large population • No gene flow • No mutations • Random mating • No natural selection – hypothetical population that is not evolving – rarely met in nature

12. Mutation and sexual recombination only sources of new variations • mutation – changes in nucleotide sequence in DNA

13. point mutations – change in one nucleotide

14. gene duplication – duplication of a chromosome segment

15. sexual recombination – crossing over, shuffling of genes during meiosis

16. Genetic Drift – change in allele frequencies due to chance • usually in smaller populations • reduces genetic variation

17. bottleneck effect –when a population has been dramatically reduced, and the gene pool is no longer reflective of the original population’s

18. Human actions can create a genetic bottleneck

19. founder effect – when a small number of individuals colonize a new area; new gene pool not reflective of original population

20. The Fugate family Kentucky's Troublesome Creek

21. gene flow – when a population gains or loses alleles • a movement of fertile individuals leaving/arriving • – a reduces differences between populations

22. genetic variation – heritable variations in a population

23. discrete characteristics – are all one discrete variety

24. quantitative characteristics – vary along a continuum, usually due to influence of two or more genes

26. average heterozygosity– measure of polymorphism in a population

27. geographic variation – difference in variation between population subgroups in different areas

28. cline – a graded change in a trait along a geographic axis

29. Evolutionary Fitness • fitness – contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals (the more offspring that you have that survive = more fit you are)

30. relative fitness – fitness of a particular genotype

31. Types of selection • directional selection – shift toward a favorable variation

32. disruptive selection • – favors the extremes

33. stabilizing selection • – favors the mean

34. Heterozygous Advantage – when individuals heterozygous • Recessive allele is maintained in the population

35. Example: sickle-cell anemia prevelence of malaria sickle-cell disease

36. Sexual selection– a natural selection for mating success

37. Sexual dimorphism – differences between the sexes in secondary sexual characteristics

38. Not necessarily better adaptations; example – mane on lion very hot, feathers on peacock very “expensive” to make

39. Common misconceptions: • Natural selection acts on phenotype, not genotype! • Natural selection does not create more perfect organisms! (what is perfect in one environment may not be perfect in another)