# Mechanisms of Evolution

## Presentation on theme: "Mechanisms of Evolution"— 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% 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