MECHANISMS FOR EVOLUTION• DO POPULATIONS OR INDIVIDUALS EVOLVE?DO POPULATIONS OR INDIVIDUALS EVOLVE?• WHAT IS A GENE POOLWHAT IS A GENE POOL• HOW CAN THE GENE POOL CHANGE?HOW CAN THE GENE POOL CHANGE?

– MUTATIONMUTATION– GENETIC DRIFTGENETIC DRIFT– GENE FLOWGENE FLOW– NON-RANDOM MATINGNON-RANDOM MATING– NATURAL SELECTIONNATURAL SELECTION

• WOULD THESE THINGS EFFECT A LARGE WOULD THESE THINGS EFFECT A LARGE POPULATION OR A SMALL POPULATION MORE?POPULATION OR A SMALL POPULATION MORE?

Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

CAUSES OF MICROEVOLUTIONMUTATIONS – 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.

GENE FLOW – genetic exchange between populations due to migration

NONRANDON MATINGBreed with other members of the

“neighborhood” promotes inbreedingAssortative mating – mate with others

like themselves . This is the premise behind artificial selection.

CAUSES OF MICROEVOLUTIONNATURAL 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 selectionDirectional selectionDisruptive selection

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Sexual SelectionSexual reproduction has evolved

independently numerous times throughout history.External InternalMotility and Numbers (sperm)Pheromones/sexual behaviors/attractants

Sexual Dimorphism – differences between males and females in looks and behaviors.

Benefits of SexIt costs a lot so why do it????

Sex creates diversity