1. Mechanisms of Evolution

2. Basic mechanisms of evolution…
Mutation
Migration
Genetic drift
Natural Selection

3. 1. Mutation
Mutations are random and sometimes result in phenotypic changes that are beneficial
eg. Green beetles may give rise to mutant brown offspring
Not all mutations matter to evolution…

4. 2. Migration Individuals possessing different alleles may intermingle
eg. A brown beetle may migrate and bring brown alleles into an exclusively green allele population

5. 3. Genetic drift
Allele frequencies fluctuate unpredictably from generation to the next
eg. In a population of green and brown beetles, the green beetles may die due to random events
eg. After World War II, returning ally soldiers started families while the losing soldiers did not

6. 3. Genetic drift
Genetic drift can sometimes dramatically effect genetic variation in large populations
Bottleneck effect – massive population loss causes the surviving alleles to be overexpressed in future generations

7. 3. Genetic drift
Genetic drift can sometimes dramatically effect genetic variation in large populations
Eg. Current elephant seal populations have reduced genetic variation because of overhunting in the 1890s (population reduced to as low as 20 individuals)

8. 3. Genetic drift
Genetic drift can sometimes dramatically effect genetic variation in large populations
Founder effect – when a new colony is started by a few members of the original population genetic variation is lost

9. 3. Genetic drift
Genetic drift can sometimes dramatically effect genetic variation in large populations
Eg. Afrikaners are a South African ethnic group descended from a handful of Dutch settlers and have an unusually high frequency of the gene that causes Huntington’s disease (because the founders carried it).

10. 4. Natural selection
Differential success in reproduction results in certain alleles being passed to the next generation in great proportions
eg. Brown beetles may evade predation while green beetles continue to be victims
eg. Peppered moths during the industrial revolution

11. 4. Natural selection cont’d
3 methods of selection:
Directional selection
Disruptive selection
Stabilizing selection

12. a) Directional selection

13. b) Disruptive selection

14. c) Stabilizing selection

15. Coevolution Often 2 (or more) species affect each other’s evolution
Examples:
Predator/prey
snow hare
lynx

16. Coevolution cont’d
Often 2 (or more) species affect each other’s evolution
Examples:
Predator/prey
Mutualistic
flower
hummingbird

17. Coevolution cont’d
Often 2 (or more) species affect each other’s evolution
Examples:
Predator/prey
Mutualistic
Competitive
black finch
red finch