| A | B |
|---|
| allele | One of two or more molecular forms of a gene that arise by mutation and code for different versions of the same trait. |
| allele frequency | For a given gene locus |
| balanced polymorphism | Form of selection in which two or more alleles for a trait are being maintained in a population over time. |
| biogeography | Scientific study of the world distribution of species. |
| bottleneck | Severe reduction in the size of a population |
| comparative morphology | Scientific study of comparable body parts of adults or embryonic stages of major lineages. |
| directional selection | Mode of natural selection by which allele frequencies underlying a range of phenotypic variation shift in a consistent direction |
| disruptive selection | Mode of natural selection by which the different forms of a trait at both ends of the range of variation are favored and intermediate forms are selected against. |
| evolution | biological |
| fitness | Increase in adaptation to environment |
| fossil | Recognizable |
| founder effect | A form of bottlenecking |
| gene flow | Microevolutionary process; alleles enter and leave a population as an outcome of immigration and emigration |
| gene pool | All genotypes in a population. |
| genetic drift | Change in allele frequencies over the generations due to chance alone. |
| genetic equilibrium | In theory |
| Hardy-Weinberg rule | Allele frequencies stay the same over the generations when there is no mutation |
| inbreeding | Nonrandom mating among close relatives that share many identical alleles. |
| lethal mutation | Mutation with drastic effects on phenotype; usually causes death |
| microevolution | Of a population |
| natural selection | Microevolutionary process; the outcome of differences in survival and reproduction among individuals that differ in details of heritable traits |
| population | All individuals of the same species that are occupying a specified area. |
| sampling error | Use of a sample or subset of a population |
| sexual selection | A microevolutionary process; a type of selection that favors a trait giving an individual a competitive edge in attracting or keeping a mate (favors reproductive success) |
| stabilizing selection | Mode of natural selection by which intermediate phenotypes in the range of variation are favored and extremes at both ends are eliminated. |
