| A | B |
|---|
| gene pool | collection of alleles found in all of the individuals of a population |
| allele frequency | proportion of one allele, compared with all the alleles for that trait, in the gene pool |
| normal distribution | distribution in a population in which allele frequency is highest near the mean range value and decreases progressively toward each extreme end |
| microevolution | observable change in the allele frequencies of a population over a few generations |
| directional selection | pathway of natural selection in which one uncommon phenotype is selected over a more common phenotype |
| stabilizing selection | pathway of natural selection in which intermediate phenotypes are selected over phenotypes at both extremes |
| disruptive selection | pathway of natural selection in which tow opposite, but equally common, phenotypes are selected over the most common phenotype |
| gene flow | physical movement of alleles from one population to another |
| genetic drift | change in allele frequencies due to chance alone, occurring most commonly in small populations |
| bottleneck effect | genetic drift that results from an event that drastically reduces the size of a population |
| founder effect | genetic drift that occurs after a small number of individuals colonize a new area |
| sexual selection | selection in which certain traits enhance mating success; traits are, therefore, passed on to offspring |
| Hardy-Weinberg equlibrium | condition in which a population's allele frequencies for a give trait do not change from generation to generation |
| reproductive isolation | final stage in speciation, in which members of isolated populations are either no longer able to mate or no longer able to produce viable offspring |
| speciation | evolution of two or more species from one ancestral species |
| behavioral isolation | isolation between populations due to differences in courtship or mating behavior |
| geographic isolation | isolation between populations due to physical barriers |
| temporal isolation | isolation between populations due to barriers related to time, such as differences in mating periods or differences in time of day that individuals are most active |
| convergent evolution | evolution toward similar characteristics in unrelated species, resulting from adaptations to similar environmental conditions |
| divergent evolution | evolution of one or more closely related species into different species; resulting from adaptations to different environmental conditions |
| coevolution | process in which two or more species evolve in response to changes in each other |
| extinction | elimination of a species from Earth |
| punctuated equilibrium | theory that states that speciation occurs suddenly and rapidly followed by long periods of little evolutionary change |
| adaptive radiation | process by which one species evolves and gives rise to many descendant species that occupy different ecological niches |
