mechanisms of evolution 1) micro-evolution –change within a species 2) macro-evolution –change...
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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%
• p2 + 2pq + q2 = 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 -> a2 -> a = (a2)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