1. 1 1 Population Genetics http://www.youtube.com/watch?v=lk4 _aIocyHc Bozeman..7:39min. http://www.youtube.com/watch?v=lk4 _aIocyHc http://www.youtube.com/watch?v=lk4 _aIocyHc

2. 2 2 Evolutionary Time Scales Long time scale events that create and destroy species. Macroevolution: Long time scale events that create and destroy species. copyright cmassengale

3. 3 3 Microevolution: Short time scale events (generation- to-generation) that change the genotypes and phenotypes of populations Evolutionary Time Scales copyright cmassengale

4. 4 4 The Gene Pool Gene pool – all of the alleles of all individuals in a population The relative frequency of an allele is the number of times that the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur.

5. 5 5 Sources of Genetic Variation Mutations: Any change in a sequence of DNA. Gene shuffling: Occurs during the production of gametes.

6. 6 6 Heritable Variation Single-gene trait: controlled by a single gene that has two alleles.( widow’s peak) Polygenic trait: controlled by two or more genes. (height)

7. 7 5 Causes of Microevolution 1. Genetic Drift - the change in the gene pool of a small population due to chance 2. Natural Selection - success in reproduction based on heritable traits results in selected alleles being passed to relatively more offspring (Darwinian inheritance) - Cause ADAPTATION of Populations 3. Gene Flow -is genetic exchange due to the migration of fertile individuals or gametes between populations 7

8. 8 Causes of Microevolution 4. Mutation - a change in an organism’s DNA - Mutations can be transmitted in gametes to offspring 5. Non-random mating - Mates are chosen on the basis of the best traits 8

9. 99 1. Genetic Drift

10. 10 Factors that Cause Genetic Drift Bottleneck Effect - a drastic reduction in population (volcanoes, earthquakes, landslides …) - Reduced genetic variation - Smaller population may not be able to adapt to new selection pressures Founder Effect - occurs when a new colony is started by a few members of the original population - Reduced genetic variation - May lead to speciation 10

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12. 12 Loss of Genetic Variation Cheetahs have little genetic variation in their gene pool This can probably be attributed to a population bottleneck they experienced around 10,000 years ago, barely avoiding extinction at the end of the last ice age 12

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14. 14 Founder’s Effect 14

15. 15 2. Natural Selection…3 modes of Nat. selection.

16. 16 Modes of Natural Selection 1.Directional Selection - Favors individuals at one end of the phenotypic range - Most common during times of environmental change or when moving to new habitats 2. Disruptive selection - Favors extreme over intermediate phenotypes - Occurs when environmental change favors an extreme phenotype 16

17. 17 Modes of Natural Selection 3.Stabilizing Selection - Favors intermediate over extreme phenotypes - Reduces variation and maintains the cureent average - Example: Human birth weight 17

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19. 19 The Hardy-Weinberg Principle States that allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change. This situation in which allele frequencies remain constant is called genetic equilibrium.

20. 20 Evolution as Genetic Change Five conditions required to maintain genetic equilibrium. a. a. Random mating d. d. No mutations b. b. Very large population e. e. No natural selection c. c. No movement into or out of the population