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gene pool

combined genetic information of all the members of a particular population

relative frequency

number of times an allele occurs in a gene pool compared with the number of times other alleles occur

single-gene trait

trait controlled by a single gene that has two alleles

polygenic trait

trait controlled by two or more genes

directional selection

when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end

stabilizing selection

form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

disruptive selection

form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

genetic drift

random change in allele frequencies that occurs in small populations

founder effect

change in allele frequencies as a result of the migration of a small subgroup of a population

Hardy-Weinberg principle

principle that allele frequencies in a population will remain constant unless one or more factors cause the frequencies to change

genetic equilibrium

situation in which allele frequencies remain constant


formation of new species

reproductive isolation

separation of species or populations so that they cannot interbreed and produce fertile offspring

behavioral isolation

form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding

geographical isolation

a form of reproductive isolation in which two populations are separated physically by geographical barriers such as rivers, mountains, or stretches of water

temporal isolation

two or more species reproduce at different times

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