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In population genetics, directional selection is a mode of natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype.
Disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the population is divided into two distinct groups.
Species: a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. The species is the principal natural taxonomic unit, ranking below a genus and denoted by a Latin binomial, e.g. Homo sapiens.
Prezygotic isolating mechanisms: Reproductive isolating mechanisms which prevent the formation of a zygote between members of different species.
Postzygotic isolating mechanisms: A mechanism that prevents interbreeding by blocking the development of a viable and fertile individual after fertilization has taken place.
Speciation: the formation of new and distinct species in the course of evolution. Speciation involves the splitting of a single evolutionary lineage into two or more genetically independent lineages.
Allopatric speciation: is speciation that occurs when biological
populations of the same species become vicariant, or isolated from each
other to an extent that prevents or interferes with genetic interchange.
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