Chapter 23 evolution of populations

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Population Genetics: Study of allele distributions and frequencies

Gene pool: All versions of all the genes carried by individuals in pop

Mutations: can cause genetic variation

Sexual reproduction: ensures genes are randomly mixed

Microevolution: Generation to generation

Hardy-Weinberg: genetic makeup we expect for pop

Natural Selection: Results in adaptation to environment

Gene flow: Transfer of alleles into or out of a population

Sexual Selection: depends on an individual's ability to obtain a mate

Phenotypic variation: results from genetic differences, environmental influences

Microevolution: can result in gradual adaptation of species to local env

Gene flow: can affect adaptations to local environments

Non-random mating: sexual selection can lead to changes in gene pool

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Hardy Weinburg

p ^2+2pq+q^2=1

p^2: Expected frequency of genotype C^rC^r

2pq: Expected frequency of genotype C^rC^w

q^2: Expected frequency of genotype C^wC^w

p2: homologous dominant frequencies

q2: homologous recessive frequencies

2pq: heterozygous frequencies

Assumptions:

1. No selection

2. No Mutations

3. No migrations

4. Large populations

5. Random mating

Change in allele frequencies may = change in phenotypic frequencies = evolution

Examples: Frequency of allele a is 0.45 for a population in HWE. What are the expected frequencies of genotypes AA, Aa, aa?

a=0.45 A=.55

AA p2=genotype freq

Aa 2pq

aa q2

Examples:

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Natural Selection

- Adaptation to environments (abiotic and biotic)

- Relative fitness: Fitness differences between different variants of traits

1. Variation - members of pop must differ

2. Inheritance - heritable differences

3. Differential adaptiveness - differences may affect adaptation

4. Differential reproduction - better adapted more likely to reproduce

Fitness: Contribution that individual makes to gene pool for next gen in comparison to others (camouflage)

Directional Selection - favors individuals at one extreme phenotype

Disruptive selection - favors individuals at both extremes

Stabilizing selection - favors intermediate variants and acts against extreme

Graph of selections

Directional: Shifted to right

Disruptive: up and down/ split

Stabilizing: skinnier

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Genetic drift: Change in gene pool due to chance

- Gene can be lost if few individuals die/migrate randomly

Bottleneck effect: Type of genetic drift involving drastic reduction in population where the surviving individuals create the next generation

Founder Effect: Few individuals migrate to new isolated habitat