MECHANISMS FOR EVOLUTION DO POPULATIONS OR INDIVIDUALS EVOLVE? DO POPULATIONS OR INDIVIDUALS EVOLVE? WHAT IS A GENE POOL WHAT IS A GENE POOL HOW CAN THE GENE POOL CHANGE? HOW CAN THE GENE POOL CHANGE? – MUTATION – GENETIC DRIFT – GENE FLOW – NON-RANDOM MATING – NATURAL SELECTION WOULD THESE THINGS EFFECT A LARGE POPULATION OR A SMALL POPULATION MORE? WOULD THESE THINGS EFFECT A LARGE POPULATION OR A SMALL POPULATION MORE? Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

CAUSES OF MICROEVOLUTION MUTATIONS – provide new alleles in a population and provide the variation for evolution to occur, should the mutation lead to some adaptive advantage. Mutation alone does not cause evolution, but provide a selective advantage that due to natural selection can lead to a shift in allele frequency.

CAUSES OF MICROEVOLUTION GENETIC DRIFT – in small populations the frequencies of alleles can be drastically affected by chance events – BOTTLENECK EFFECT – if populations are driven to the point of extinction the remaining individuals do not carry a true representation of the original gene pool. – FOUNDER EFFECT – when a small number of individuals colonize a new area they only carry with them a small representation of the total number of the alleles from the gene pool.

GENETIC DRIFT

BOTTLENECK EFFECT

FOUNDER EFFECT

GENE FLOW – genetic exchange between populations due to migration NONRANDON MATING Breed with other members of the “neighborhood” promotes inbreeding Assortative mating – mate with others like themselves. This is the premise behind artificial selection.

CAUSES OF MICROEVOLUTION NATURAL SELECTION – any environmental factor that leads to a particular allele having some adaptive advantage. There are three ways that natural selection can affect the frequency of traits: Stabilizing selection Directional selection Disruptive selection Page 693

Sexual Selection Sexual reproduction has evolved independently numerous times throughout history. External  Internal Motility and Numbers (sperm) Pheromones/sexual behaviors/attractants Sexual Dimorphism – differences between males and females in looks and behaviors.

Benefits of Sex It costs a lot so why do it???? Sex creates diversity