1. 1 1 Population Genetics

2. 2 Genes Within Populations Chapter 16

3. 3 3 1. The Gene Pool a. Members of a species can interbreed & produce fertile offspring b. Species have a shared gene pool

4. 4 4 The Gene Pool 2. Different species do NOT exchange genes by interbreeding Example: Different species that can interbreed - =produce sterile or less viable offspring e.g. Mule

5. 5 5 Populations A group of the same species living in an area No two individuals are exactly alike (variations) More Fit individuals survive & pass on their traits

6. 6 6 Speciation Definition: Formation of new species a. One species may split into 2 or more species b. species may evolve into a new species Requires very long periods of time

7. 7 7 Five Agents of Evolutionary Change Selection pressures: avoiding predators matching climatic condition pesticide resistance

8. 8 Modern Evolutionary Thought

9. 9 9 Modern Synthesis Theory Combines Darwinian selection and Mendelian inheritance Combines Darwinian selection and Mendelian inheritance Population genetics - study of genetic variation within a population Population genetics - study of genetic variation within a population Emphasis on quantitative characters Emphasis on quantitative characters

10. 10 Modern Synthesis Theory Today’s theory on evolution Recognizes that GENES are responsible for the inheritance of characteristics Recognizes that POPULATIONS, not individuals, evolve due to natural selection & genetic drift Recognizes that SPECIATION usually is due to the gradual accumulation of small genetic changes

11. 11 Describing genetic structure genotype frequencies allele frequencies rr = white Rr = pink RR = red

12. 12 Why is genetic variation important? adaptation to environmental change - conservation Genetic variation in space and time divergence of populations - biodiversity

13. 13 variation no variation north south north south

14. 14 Why is genetic variation important? variation no variation EXTINCTION!! global warming survival

15. 15 Why is genetic variation important? variation no variation divergence NO DIVERGENCE!! north south north south

16. 16 Microevolution Changes occur in gene pools due to a.mutation, b.natural selection, c.genetic drift. Gene pool changes cause more VARIATION in INDIVIDUALS in the population This process is called MICROEVOLUTION Example: Bacteria becoming unaffected by antibiotics (resistant)

17. 17 Species & Populations Population Population - a localized group of individuals of the same species. Species Species - a group of populations whose individuals have the ability to breed and produce fertile offspring. Gene Pool is defined by TOTAL GENES

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19. 19 Gene Pools gene pool A population’s gene pool composed of the total # all genes in the population at any time. If all members of a population are #11. ) homozygous for a particular allele, then the allele is fixed in the gene pool.

20. 20 The Hardy-Weinberg Theorem non-evolving population. Used to describe a non-evolving population. Shuffling of alleles by meiosis and random fertilization have no effect on the overall gene pool. Natural populations are NOT expected to actually be in Hardy- Weinberg equilibrium.

21. 21 Assumptions of the H-W Theorem a.Large population size - small populations have fluctuations in allele frequencies (e.g., fire, storm). b.No migration - immigrants can change the frequency of an allele by bringing in new alleles. c. No net mutations - if alleles change from one to another, this will change the frequency of those alleles.

22. 22 Assumptions of the H-W Theorem d. Random mating - if certain traits are more desirable, then individuals with those traits will be selected e. No natural selection.

23. 23 Hardy-Weinberg Equilibrium The Hardy-Weinberg Equation: 1.0 = p 2 + 2pq + q 2 where p 2 = frequency of AA genotype; 2pq = frequency of Aa q 2 = frequency of aa genotype

24. 24 Hardy-Weinberg Equilibrium

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27. 27 Evolution within a species or a population is microevolution. Microevolution refers to changes in allele frequencies in a gene pool and represents a change in a population.

28. 28 a) Genetic Drift b) Gene flow c) Natural Selection d) Mutations non-random mating #18. Changes in allele frequencies How does genetic structure change? Causes of Microevolution

29. 29 1) Genetic drift Genetic drift = the alteration of the gene pool of a small population due to chance. Two factors may cause genetic drift:

30. 30 19 Bottleneck effect leads reduces genetic variability following a large disturbance such as an earthquake that removes a large portion of the population. The surviving population often does not represent the Original

31. 31 20) Founder effect may lead to reduced variability when a few individuals from a large population colonize an isolated habitat.

32. 32 Genetic drift 8 RR 8 rr Before: After: 2 RR 6 rr 0.50 R 0.50 r 0.25 R 0.75 r

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35. 35 Genetic Drift - Bottleneck Effect

36. 36 Natural selection Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant

37. 37 Natural selection Generation 1: 1.00 not resistant 0.00 resistant Resistance to antibacterial soap

38. 38 Natural selection Resistance to antibacterial soap mutation! Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant

39. 39 Natural selection Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant Generation 3: 0.76 not resistant 0.24 resistant

40. 40 Natural selection Resistance to antibacterial soap Generation 1: 1.00 not resistant 0.00 resistant Generation 2: 0.96 not resistant 0.04 resistant Generation 3: 0.76 not resistant 0.24 resistant Generation 4: 0.12 not resistant 0.88 resistant

41. 41 *Yes, I realize that this is not really a cheetah.

42. 42 2) Natural selection As previously stated, differential success in reproduction based on heritable traits results in selected alleles being passed to relatively more offspring (Darwinian inheritance). The only agent that results in adaptation to environment. 3) Gene flow -is genetic exchange due to the migration of fertile individuals or gametes between populations.

43. 43 4) Mutation Mutation is a change in an organism’s DNA and is represented by changing alleles. a. Mutations can be transmitted in gametes to offspring, and immediately affect the composition of the gene pool. b. The original source of variation and the driving force for Natural Selection

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45. 45 Genetic Variation, the Substrate for Natural Selection Genetic (heritable) variation within and between populations: exists both as what we can see (e.g., eye color) and what we cannot see (e.g., blood type). Not all variation is heritable. Environment also can alter an individual’s phenotype.

46. 46 Industrial Melanism of Butterfly Population Industrial Melanism

47. 47 Variation between populations Geographic variations are differences between gene pools due to differences in environmental factors. It often occurs when populations are located in different areas, but may also occur in populations with isolated individuals.

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49. 49 Mutation and sexual recombination generate genetic variation a. New alleles originate only by mutations (heritable only in gametes; many kinds of mutations; mutations in functional gene products most important). - Mutations are more beneficial (rare) in changing environments. (Example: HIV resistance to antiviral drugs.) b. Sexual recombination is the source of most genetic differences between individuals in a population.

50. 50 Diploidy and balanced polymorphism preserve variation a. Diploidy often hides genetic variation from selection in the form of recessive alleles. Dominant alleles “hide” recessive alleles in heterozygotes. b. Balanced polymorphism is the ability of natural selection to maintain stable frequencies of at least two phenotypes. Heterozygote advantage is one example of a balanced polymorphism, where the heterozygote has greater survival and reproductive success than either homozygote (Example: Sickle cell anemia where heterozygotes are resistant to malaria).

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52. 52 Diversifying selection

53. 53 Sexual selection leads to differences between sexes a. Sexual dimorphism is the difference in appearance between males and females of a species. -Intrasexual selection is the direct competition between members of the same sex for mates of the opposite sex. -This gives rise to males most often having secondary sexual equipment such as antlers that are used in competing for females. -In intersexual selection (mate choice), one sex is choosy when selecting a mate of the opposite sex. -This gives rise to often amazingly sophisticated secondary sexual characteristics; e.g., peacock feathers.

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56. 56 Sickle Cell and Malaria

57. 57 Evolutionary Change in Spot Number

58. 58 Population genetics – Outline What is population genetics? Calculate Why is genetic variation important? - genotype frequencies - allele frequencies How does genetic structure change?

59. 59 Example use of H-W theorem 1000-head sheep flock. No selection for color. Closed to outside breeding. 910 white (B_) 90 black (bb)

60. 60 Start with known: f(black) = f(bb) =.09 =q 2 Then, p = 1 – q =.7 = f(B) f(BB) = p 2 =.49 f(Bb) = 2pq =.42 f(bb) = q 2 =.09

61. 61 In summary: Allele freq. f(B) = p =.7 (est.) f(b) = q =.3 (est.) Phenotypic freq. f(white) =.91 (actual) f(black) =.09 (actual) Genotypic freq. f(BB) = p 2 =.49 (est.) f(Bb) = 2pq =.42 (est.) f(bb) = q 2 =.09 (actual)

62. 62 Mink example using H-W Group of 2000homo (1920 brown, 80 platinum) in equilibrium. We know f(bb) = 80/2000 =.04 = q 2 f(b) =  (q 2 ) = .04 =.2 f(B) = p = 1- q =.8 f(BB) = p 2 =.64 f(Bb) = 2pq =.32