1. Population Evolution Ch.16

2. (16-1) Population Genetics Study of evolution from a genetic point of view Population: individuals of the same species that interbreed

3. Populations Variations w/in a pop. –Bell shaped curve

4. How to get Variations Genetic factors –Mutations –Recombination (crossing-over & indep. assortment) –Random fusion of gametes (fertilization) Environmental factors

5. Definitions Gene pool: total genetic info in a pop. Allele frequency: how often a certain allele occurs in the gene pool –# of certain alleles / total # of alleles in pop.

6. Definitions (cont.) p = freq. of dominant allele q = freq. of recessive allele Phenotype frequency: # of individuals w/ a particular phenotype / total # of individuals

7. Hardy-Weinberg Equation p 2 + 2pq + q 2 = 1 p 2 = ho/go dominant 2pq = he/go q 2 = ho/go recessive

10. Hardy-Weinberg Equilibrium Allele frequencies remain constant over time (no evolution) Pop. in H-W equil. when certain assumptions are held…

11. H-W Assumptions 1.Random mating 2.No selective advantage of genotypes (no natural selection) 3.No mutations 4.No migration of individuals 5.Large pop. size

13. How This Relates to Evolution? Evolution occurs when there’s a disruption of equil.

14. (16-2) Causes of Equilibrium Disruptions 1.Mutation 2.Migration 3.Genetic drift 4.Nonrandom mating 5.Natural selection

15. Mutation Occur at low rates Mutagen: mutation-causing agent –Radiation –Chemicals Can produce new alleles in a pop. –Most are harmful

16. Migration Immigration: movement into a pop. Emigration: movement out of a pop. Gene flow: genes moving from 1 pop. to another

17. Genetic Drift Allele freq. in a pop. change as a result of random events or chance –Very significant in small pops. Ex: old-order Amish & genetic disorders

18. Nonrandom Mating Mate selection based upon: –Geographic area –Physical characteristics Assortive mating

19. Sexual Selection Choosing a mate based on certain traits –In order to leave offspring male must be selected by female Genes of successful reproducers, rather than those of successful survivors are amplified by natural selection

20. Natural Selection 3 types: 1. Stabilizing 2. Directional 3. Disruptive

21. Stabilizing Selection Individuals w/ the average form of a trait is the most fit

22. Directional Selection Individuals that display a more extreme form of a trait have the highest fitness

23. Disruptive Selection Individuals w/ either extreme variation of a trait have the greater fitness than the avg. of the trait

24. (16-3) Formation of Species Speciation: species formation Morphology: internal & external structure & appearance of an organism –Used for classification

25. Biological Species Concept A pop. of organisms can successfully interbreed but cannot breed w/ other groups Modern definition of species includes both morphology & biological species concept

26. Isolating Mechanisms Speciation begins w/ isolation 2 important types: –Geographic isolation –Reproductive “

27. Geographic Isolation Physical separation of members of a pop. –Ex: canyon develops through habitat Leads to allopatric speciation

28. Reproductive Isolation Results from barriers (not physical) to successful breeding b/w pop. groups in the same area 2 types: –Prezygotic: before fertilization Difference in mating times –Postzygotic: after fertilization Offspring may be unhealthy or infertile

30. Rates of Speciation Gradualism –Species develop by consistent & slow evolution Punctuated equilibrium –Stops & starts in evolution in response to dramatic environmental changes cause speciation

31. Gradualism

32. Punctuated Equilibrium