How populations change over time Population Genetics How populations change over time

Hardy-Weinberg States that without outside factors acting on a population, allele frequencies would remain the same = NO EVOLUTION Factors affecting evolution: Genetic drift Gene flow Nonrandom mating Mutations Natural selection

Genetic Drift ANY change in allele frequencies Founder Effect: occurs when a small sample of the population is separated from the rest Bottleneck Effect: Population declines to a very low number and then rebounds BOTH RESULT IN Organisms breed with one another Might see new/uncommon traits emerge

Gene Flow Individuals are always moving into and out of habitats based on competition and/ or predation Immigration and emigration Causes NEW allele frequencies

Gene Flow Introduced species Purple loosestrife, originally brought to North America accidentally on cargo ships, reproduces very quickly and aggressively, often crowding out species like the cattail.

Nonrandom Mating Organisms mate with individuals in close proximity  promotes inbreeding Could lead to a change in allele frequencies (mutations)

Nonrandom Mating ALSO includes sexual selection  mate chosen based on “best” genes Mating call/dance Gifts Fighting

Mutation Random change in genetic material May be harmful or lethal Might ALSO be beneficial

Natural Selection Acts to select the individuals that are best adapted to their environment Changes allele frequencies and phenotype Stabilizing: neither extreme is good  human baby weight Directional: influenced by environment Peppered Moth’s response to pollution Disruptive: both extremes work for different habitats  retains individuals expressing extreme traits

Speciation Species diverge when they are isolated Allopatric ( physical barrier) Sympatric (no physical barrier)

Rate of Speciation Punctuated Equilibrium Gradualism