What leads to variation among species?

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

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

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

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

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.

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!

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

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.

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

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

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

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

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

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

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

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