Biology Chapter 17: The Means Of Evolution

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A group of actually or potentially interbreeding natural populations that are reproduc-tively isolated from other such populations.

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species

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All the members of a species that live in a defined geographic region at a given time.

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population

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The genetic makeup of an organism, including all the genes that lie along its chromosomes.

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genotype

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A physical function, bodily characteristic, or action of an organism.

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phenotype

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One of the alternative forms of a single gene. In pea plants, a single gene codes for seed color, and it comes in two alleles—one codes for yellow seeds, the other for green seeds.

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allele

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The entire collection of alleles in a population.

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gene pool

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A change of allele frequencies in a population over a short period of time. The basis for all large-scale or macroevolution.

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microevolution

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Any genetically based phenotypic change in a population of organisms over successive generations.

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evolution

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Evolution that results in the formation of new species or other large groupings of living things.

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macroevolution

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The movement of genes from one population to another.

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gene flow

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A regular movement of animals from one location to a distant location.

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migration

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The chance alteration of allele frequencies in a population, with such alterations having greatest impact on small populations.

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genetic drift

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A change in allele frequencies in a population due to chance following a sharp reduction in the population's size. One of the factors that potentiates genetic drift.

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bottleneck effect

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The phenomenon by which an initial gene pool for a population is established by means of that population migrating to a new area. One of the conditions that potentiates genetic drift.

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founder effect

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A form of natural selection that produces differential reproductive success based on differential success in obtaining mating partners.

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sexual selection

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A process in which the differential adaptation of organisms to their environment selects those traits that will be passed on with greater frequency from one generation to the next.

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natural selection

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a modification in the form, physical functioning, or behavior of organisms in a population over generations in response to environmental change.

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adaptation

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In evolution, the success of an organism, relative to other members of its population, in passing on its genes to offspring.

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fitness

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Having multiple genes affecting a given character, such as height in humans.

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polygenic

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In evolution, the type of natural selection in which intermediate forms of a given character are favored over either extreme. This process tends to maintain average traits for a character.

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stabilizing selection

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In evolution, the type of natural selection that moves a character toward one of its extremes.

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directional selection

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In evolution, the type of natural selection that moves a character toward both of its extremes, operating against individuals that are average for that character. This type of selection seems to be less common in nature than either stabilizing or directional selection.

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disruptive selection