The Death of a Gene

When a gene is duplicated, the new copy is often dead-on arrival (lacks the regulatory elements). 

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Relative genotypic frequency after selection

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Positive Selection: The Spread of Beneficial Mutations

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There are three basic modes of selection on a quantitative trait.

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Overdominance the heterozygote has higher fitness than the  fitnesses of the two homozygotes

Underdominance, in which the heterozygote has lower fitness than both homozygotes.

Directional selection leads to fixation of the favored allele and elimination of the other allele, as  long as no other evolutionary forces act on the population.

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Artificial selection- Genetically improving animals and plants by breeding together the best individuals in their fields and flocks.

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Types of selection