 | Term | Definition |
| |
neutral variation |
The theory that some of the genetic variation in populations probably has little or no impact on reproductive success, and thus natural selection doesn't affect those alleles. |
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adaptive evolution |
An evolutionary process that is directed by natural selection, which makes a population better adapted to live in an environment. |
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relative fitness |
The average number of surviving progeny of a particular genotype compared with average number of surviving progeny of competing genotypes after a single generation. |
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selection coefficient |
The proportion by which the fitness of a genotype is less than the fitness of a standard genotype, which is usually the genotype with the highest fitness. |
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pleiotropy |
A single gene that has multiple effects on a given individual's phenotype. |
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stabilizing selection |
Selection where intermediate forms are favored and extreme forms are eliminated. |
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directional selection |
Selection where one extreme is favored and therefore the phenotype of the population shifts toward that extreme. |
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diversifying selection |
Selection where both extremes of the distribution are favored and the intermediates are exterminated. |
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sexual dimorphism |
Differences in physical characteristics between males and females of the same species. |
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sexual selection |
Selection where preferential mating with one or more genotypes causes changes in the gene pool of the population. |
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polymorphism |
The occurrence in a population (or among populations) of several phenotypic forms. |
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geographical variation |
Differences in genetic structure between populations. |
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balanced polymorphism |
Maintenance of two or more alleles in a population due to the selective advantage of the heterozygote |
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heterozygote advantage |
Greater reproductive success of heterozygous individuals compared to homozygotes; tends to preserve variation in gene pools. (i.e. sickle cell disease) |
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frequency-dependent selection |
An evolutionary process where the fitness of a phenotype is dependent on its frequency relative to other phenotypes in a given population. In positive frequency dependent selection, the fitness of a phenotype increases as it becomes more common. In negative frequency dependent selection, the fitness of a phenotype increases as it becomes less common. |
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Batesian mimicry |
A type of mimicry in which a harmless species looks like a species that is poisonous or otherwise harmful to predators. |
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species |
A group of populations with the ability to interbreed producing viable and fertile offspring. |
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gene flow |
The exchange of genes with another population. |
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gene pool |
The sum total of genes, with all their variations, possessed by a particular species at a particular time. |
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fixed allele |
Where all the members of a population are homozygous for that allele. |
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microevolution |
Evolution resulting from a succession of relatively small genetic variations between generations that often cause the formation of new subspecies. |
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Hardy-Weinberg equilibrium |
Allele frequencies in a population tend to remain the same from generation to generation unless acted on by outside influences. |
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bottleneck effect |
Genetic drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is no longer genetically representative of the original population. |
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founder effect |
When a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool isn't reflective of the source population. |
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inbreeding |
A breeding method in which closely related individuals are mated to retain or strengthen certain desirable traits. |
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assortative mating |
Nonrandom mating on the basis of phenotype; usually used for positive assortative mating, the propensity to mate with others of like phenotype. |
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polygenic traits |
A trait controlled by two or more genes. |
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absolute fitness |
The ratio between the number of individuals with that genotype after selection to those before selection. |
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