Presentation on theme: "Mechanisms of Evolution"— Presentation transcript:
1 Mechanisms of Evolution 1) Micro-evolutionchange within a species2) Macro-evolutionchange between species
2 Micro-evolutionHardy-Weinberg (2 mathmaticians)“Frequency of alleles in a population stays the same generation after generation unless acted upon by some outside force.”So, what kind of things can change the frequency of alleles in a population?
3 Hardy-Weinberg (Cont) All alleles contribute by males (p+q)All alleles contributed by females (p+q)Together males and females mate(p+q)(p+q) = 1all combinations =100%p2 + 2pq + q2 = 1 (Also show Punnett)
4 Hardy-Weinberg (Cont) The p = Allele F = Free EarlobesThe q = Allele a = Attached earlobesSince q (or a) is the only phenotype with a known genotype (aa), then we can calculate the frequencies of alleles in a populationaa -> a2 -> a = (a2)1/2F = 1-a (since both a and F = 100%)
5 Hardy-WeinbergFor a Non-Evolving population, these conditions must be met:1) No mutations2) No migration3) No Genetic Drift-Population Large4) Random Mating5) No Natural Selection
6 If a population changes (gene frequency) or evolves, it must be due to some factor that violates one of the conditions stated previously.
7 Gene Flow: Alleles introduced to a gene pool 1) Mutation2) Migration (immigration/emigration)Animals leave area for anothercontribute genes to neighbor’s gene poolPlants have seeds dispersed by high winds
8 Immigration/Emigration Very Common2nd only to Natural Selection as cause of evolution
9 Conflicting Forces Gene flow - increase similarity between populations Natural Selection - decrease similarity between populationsPossible Outcome:gradient of variation from one population to anotherIncrease distance = increase variation
13 Genetic Drift: Evolution by chance 1) Bottleneck Effect: Most of the population is destroyed by a natural event (volcano, earthquake, etc.) and a few individuals survive to reproduce2) Founder Effect: Few people leave an area to colonize new area
14 Good chance not carry representative sample of all genes present in original population Environment is differentdifferent selection pressuresTherefore, evolve in new direction
15 In practice, difficult to tell how much of genetic differences between old and new populations is due to:1) Founders effect2) Different selection pressures in two environments
16 Founder Effect is great 1) Population of plants that populate an island from a single seed2) Animals which have descended from one original wild femaledomestic hamsters
17 Mating Preferences Females consistently choose one trait over another Exert selection pressure for one genetails of peacocks
18 Female preferences is a form of Natural Selection One genotype has reproductive advantage over another