Chapter 18.txt

[L. adaptare, to fit] Any long-term, heritable aspect of form, function, or behavior that improves an individual�s chances of surviving and reproducing; outcome of natural selection and other microevolutionary processes.

Abundance of one allele relative to others at a gene locus among individuals of a population.

One of two or more molecular forms of a gene at a given locus; alleles arise by mutation and encode slightly different versions of the same trait.

An outcome of natural selection against homozygotes, so that two or more alleles for a trait are being maintained in the population.

Severe reduction in the size of a population, brought about by intense selection pressure or a natural calamity.

Persistence of two forms of the same trait in a population.

Mode of natural selection by which forms at one end of a range of phenotypic variation are favored.

Mode of natural selection that favors different forms of a trait at both ends of a range of variation; intermediate forms are selected against.

Permanent move of one or more individuals out of a population.

[L. evolutio, an unrolling] Genetic change in a line of descent by microevolutionary events (gene mutation, natural selection, genetic drift, and gene flow); basis of large-scale patterns, rates, and trends in the history of life.

Of a population, the loss of all alleles but one at a gene locus; all individuals have become homozygous for the allele.

A form of bottlenecking. By chance, a few individuals that establish a new population differ in allele frequencies relative to the original population.

Microevolutionary process; alleles enter and leave a population by immigration and emigration. Counters mutation, natural selection, and genetic drift, hence reproductive isolation.

Small-scale change in the nucleotide sequence of a gene; can result in an altered protein product.

Change in allele frequencies over generations due to chance alone. Most pronounced effects in small populations.

In theory, a state in which a population is not evolving with respect to a specified gene locus. Compare Hardy�Weinberg rule.

Theoretical baseline for tracking changes in allele frequencies over the generations. Frequencies do not change as long as there is no mutation, the population is infinitely large and isolated from other populations, and all individuals are reproducing equally and randomly.

One or more individuals move and take up residence in another population of its species.

Nonrandom mating among very close relatives that share many identical alleles; may fix harmful alleles.

Mutation having drastic effects on phenotype; usually causes death.

Of a population, a smallscale change in allele frequencies resulting from mutation, genetic drift, gene flow, natural selection, or a combination of them.

A mutation with no effect on phenotype; natural selection thus cannot change its frequency in a population.

[Gk. polus, many,+morphe, form] Persistence of two or more qualitatively different forms of a trait, or morphs, in a population.

All individuals of the same species living in a specified area.

The odds that each outcome of an event will occur is proportional to the total number of ways in which that outcome can be reached.

A notable difference between female and male phenotypes of a population.

A category of natural selection; an outcome of differences in success at attracting mates and reproducing among individuals of a population.

Mode of natural selection; intermediate phenotypes are favored over extremes at both ends of the range of variation.