1. What leads to variation among species?

2. Mechanisms of Evolution
1. Natural Selection
2. Mutation
3. Genetic Drift
4. Gene Flow/Migration
5. Non-Random Mating

3. 1. Natural Selection
Conditions in nature determine which organisms survive and reproduce.

4. 2. Mutations
Changes in DNA sequences that can result from environmental factors (chemical exposure/ radiation) or simply by chance

5. Mutation Cont’d… Can lead to no change in phenotype
When the mutation occurs on a stretch of DNA that does not code for anything
Can lead to small changes in phenotype
When cat’s ear has a slight curl
Can lead to big changes in phenotype
Death

6. Gene Pool A collection of genes for all the traits in a population
If gene mutations persist, they may become a standard part of that gene pool.

7. 3. Genetic Drift
Affects the genetic make-up of a population through an entirely random process
“Lucky” individuals survive, not necessarily the healthier or more “fit” individuals.
May decrease genetic
diversity!

8. 4. Gene Flow Also called Migration
Movement of individuals into or out of a population
Mobility affects gene flow so animals have a higher rate of gene flow then plants.
Examples: People moving to a new city

9. Reasons for Migration Overcrowding of organisms in one area
Lack of food/water
Reproduction
Ex. Male lions migrate before reaching maturity. If the lion leaves, it’s genetic make-up will be lost from its original population, but will be added to a new population.

10. 5. Non-Random Mating
Occurs when certain individuals have less chance to mate and tend to be eliminated from the population.
Common in species that choose their mates
Non-Random = specific preference

11. Mechanisms for Evolutionary Change
1. Natural Selection
2. Mutation
3. Genetic Drift
4. Gene Flow/Migration
5. Non-Random Mating

13. Divergent vs. Convergent Evolution
Patterns of Evolution
Divergent vs. Convergent Evolution

14. Divergent Evolution
When related species evolve away from their common ancestors to become more successful in their niches.
Homologous structures (vertebrate forearms)
Finches
Red Fox - Woods
Kit Fox - Desert

15. Convergent Evolution
Species that are not closely related independently evolve similar traits.
Analogous structures (fly wing vs. bird wing)

16. Convergent Evolution
The fusiform body shape has evolved several times in very different organisms.

17. *Divergent evolution is to homologous structures as convergent evolution is to analogous structures

18. Question:
Are the shells of turtles and snails examples of convergent or divergent evolution? Explain your answer.