Why Is Outcrossing So Common in Nature?
Most eukaryotes are capable of sexual reproduction, and in most species outcrossing is preferred to close inbreeding. Examples of close inbreeding are self-fertilization in plants, and consanguineous marriages (cousin marriages) or Incest in humans. The main selective advantage of outcrossing compared to inbreeding appears to be that outcrossing promotes the masking of deleterious recessive alleles or “complementation”, while inbreeding promotes their harmful expression. For example, in humans, consanguineous marriages lead to children with increased heart malformations and increased mortality. In another example, from a different species, the inbreeding of mice derived from wild populations was found to significantly reduce survival when such mice were reintroduced into a natural habitat.
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