Presentation on theme: "Mechanisms of Evolution 1) Micro-evolution –change within a species 2) Macro-evolution –change between species."— Presentation transcript:
Mechanisms of Evolution 1) Micro-evolution –change within a species 2) Macro-evolution –change between species
Micro-evolution Hardy-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?
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) = 1 –all combinations =100% p 2 + 2pq + q 2 = 1 (Also show Punnett)
Hardy-Weinberg (Cont) The p = Allele F = Free Earlobes The q = Allele a = Attached earlobes Since q (or a) is the only phenotype with a known genotype (aa), then we can calculate the frequencies of alleles in a population aa -> a 2 -> a = (a 2 ) 1/2 F = 1-a (since both a and F = 100%)
Hardy-Weinberg For a Non-Evolving population, these conditions must be met: 1) No mutations 2) No migration 3) No Genetic Drift-Population Large 4) Random Mating 5) No Natural Selection
If a population changes (gene frequency) or evolves, it must be due to some factor that violates one of the conditions stated previously.
Gene Flow: Alleles introduced to a gene pool –1) Mutation –2) Migration (immigration/emigration) Animals leave area for another –contribute genes to neighbor’s gene pool Plants have seeds dispersed by high winds
Immigration/Emigration –Very Common –2nd only to Natural Selection as cause of evolution
Conflicting Forces Gene flow - increase similarity between populations Natural Selection - decrease similarity between populations Possible Outcome: –gradient of variation from one population to another –Increase distance = increase variation
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 reproduce 2) Founder Effect: Few people leave an area to colonize new area
–Good chance not carry representative sample of all genes present in original population –Environment is different different selection pressures Therefore, evolve in new direction
–In practice, difficult to tell how much of genetic differences between old and new populations is due to: 1) Founders effect 2) Different selection pressures in two environments
–Founder Effect is great 1) Population of plants that populate an island from a single seed 2) Animals which have descended from one original wild female –domestic hamsters
Mating Preferences Females consistently choose one trait over another –Exert selection pressure for one gene tails of peacocks
–Female preferences is a form of Natural Selection One genotype has reproductive advantage over another