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Chapter 6

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


Department
Biology
Course Code
BIOL150
Professor
Rebecca Rooney
Chapter
6

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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
Random
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
heterozygotes
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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