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Chapter 6

BIOL150 Chapter Notes - Chapter 6: Phenotypic Trait, Assortative Mating, Panmixia

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Rebecca Rooney

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Biology 150 Chapter 6 Hardy-Weinberg Equilibrium and Exceptions
Organismal and Evolutionary Ecology Reading notes
6.1 Evolutionary Processes: Various Processes Disrupt the Hardy-Weinberg Equilibrium
- 5 criteria are met that both allele and genotype frequencies remain unchanged in
successive generations of a sexually reproducing population
(1) No natural selection
(2) Low/no mutation
(3) Large population so that no genetic drift
(4) No net movement of individuals (no migration)
(5) Random mating
- Mutations: heritable change in the structure of genes or chromosomes
The mutation rate is affected by many factors, eg UV radiation
Might be beneficial, neutral or harmful
Can alter allele frequencies
- Genetic Drift: changes in allele frequencies that occur in small populations
2 situations in which genetic drift is important
(1) when a few individuals colonize an area, their genetic composition can
have a long-lasting founder effect on the resident population. Colonizing
ability does not necessarily correlate with traits that improve fitness in
the new environment, if there is a large element of chance involved in
which individuals colonize
(2) evolutionary bottle-neck effect: results when a disturbance wipes out
most of a population, leaving a few individuals from which the population
re-establishes. If a population remains small after a bottleneck, it is
vulnerable to further genetic drift. Even if the population recovers, its
genetic diversity if often reduced, increasing its vulnerability to
environmental change
- Gene Flow: movement of genes between populations as a result of migration
If an individual moves into a population but does not successfully reproduce,
its genes are not introduced into the gene pool
In circumstances where individuals do reproduce, migration is a potent force
in reducing genetic differences among local populations (assuming their
genetic composition differs)
- Non-random mating
Assortative (non-random) mating: they choose mates non-randomly based
on a phenotypic trait, apply to animals, even plants and fungi
Female mate choiceinvolves a female bias towards mates based on specific
phenotypic traits such as body size or markings
Positive assortative mating: mates are phenotypically more similar than
expected by chance, increases the frequency of homozygotes over
Negative assortative mating: mates are phenotypically less similar than
expected by chance, less common than positive assortative mating, increases
the frequency of heterozygotes
- Whether positive or negative, assortative mating changes genotypic frequencies
between generations but does not directly alter allele frequencies
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