1. Mechanisms for Genetic Variation

2. Population A localized group of individuals of the same species.

3. Species A group of similar organisms. A group of populations that could interbreed and produce fertile offspring.

4. Microevolution Caused by violations of the five H-W assumptions.

5. Causes of Microevolution 1. Genetic Drift 2. Gene Flow 3. Mutations 4. Nonrandom Mating 5. Natural Selection

6. 1. Genetic Drift Changes in the gene pool of a small population by chance. Change can be drastic (especially in small populations) Types: 1. Bottleneck Effect 2. Founder's Effect

7. By Chance

8. Bottleneck Effect Loss of most of the population by disasters. Surviving population may have a different gene pool than the original population.

10. Result Some alleles lost. Other alleles are over-represented. Genetic variation usually lost.

11. Importance Reduction of population size may reduce gene pool for evolution to work with. Ex: Northern elephant seals - over hunting reduced numbers to 20.

12. Founder's Effect Genetic drift in a new colony that separates from a parent population. Probably accounts for the relatively high frequency of certain inherited disorders among isolated human populations

13. Result Genetic variation reduced. Some alleles increase in frequency while others are lost (as compared to the parent population). Very common on islands Ex. High occurrence of a progressive form of blindness (recessive disorder) on an island populated by 15 colonists

14. 2. Gene Flow Movement of genes in/out of a population. Ex: Immigration Emigration

15. Result Changes in gene frequencies. Tends to reduce differences between populations.

16. 3. Mutations Inherited changes in a gene.

17. Result May change gene frequencies (small population). Source of new alleles for selection. Often lost by genetic drift.

18. 4. Nonrandom Mating Failure to choose mates at random from the population.

19. Causes Inbreeding within the same “neighborhood”. Assortative mating (like with like). Choose partners that have a similar phenotype (ex. size) Basis for artificial selection (animals breed for specific characteristics)

20. Result Increases the number of homozygous loci. Does not in itself alter the overall gene frequencies in the population.

21. 5. Natural Selection Differential success in survival and reproduction. Result - Shifts in gene frequencies. Selective pressures (predation, competition, etc.) work on populations, and consequently some individuals are more likely to survive and reproduce than others

22. As the Environment changes, so does Natural Selection and Gene Frequencies.

23. Of all the factors that can change a gene pool, only natural selection is likely to adapt a population to its environment. Natural selection accumulates and maintains favourable genotypes in a population Depends on the existence of genetic variation

24. Examples Garter SnakesGaillardia

25. Sources of Genetic Variation Mutations. Recombination though sexual reproduction. Crossing-over Random fertilization

26. Rate of Selection Differs between dominant and recessive alleles. Selection pressure by the environment.

27. Modes of Natural Selection 1. Stabilizing 2. Directional 3. Diversifying 4. Sexual

29. Stabilizing Selection toward the average and against the extremes. Ex: birth weight in humans

30. Directional Selection Selection toward one extreme. Common during times of change Ex: running speeds in race animals. Ex. modern horse

31. Diversifying Selection toward both extremes and against the norm. Can lead to intermediate being eliminated from the population Ex: bill size in birds

32. Sexual Mate selection Differential reproductive success that results from variation in the ability to obtain mates May not be adaptive to the environment, but increases reproduction success of the individual.

33. Result Sexual dimorphism (differences in form between members of the opposite sex) Secondary sexual features for attracting mates.

34. Comments Females may drive sexual selection and dimorphism since they often "choose" the mate.