Everything about Inbreeding Depression totally explained
Inbreeding depression is reduced
fitness in a given
population as a result of breeding of related individuals. Breeding between closely related individuals, called
inbreeding, results in more
recessive deleterious traits manifesting themselves. The more closely related the breeding pair is, the more
homozygous deleterious
genes the offspring may have, resulting in very unfit individuals. Another mechanism responsible is
overdominance of heterozygous alleles leading to a reduction in the fitness of a population with many homozygous genotypes, even if they're not deleterious. Currently it isn't known which of the two mechanisms is more important. In general, populations with more genetic variation don't suffer from
inbreeding depression. Inbreeding depression is often the result of a
population bottleneck. Inbreeding depression seems to be present in most groups of organisms, but is perhaps most important in
hermaphroditic species, most prominently in plants. The majority of plants are hermaphroditic and thus are capable of the most severe degree of inbreeding.
Inbreeding depression and natural selection
Natural selection can't effectively remove all deleterious recessive genes from a population for several reasons. First, deleterious genes arise constantly through mutation within a population. Second, in a population where inbreeding occurs frequently, most offspring will have some deleterious traits, so few will be more fit for survival than the others. It should be noted, though, that different deleterious traits are extremely unlikely to equally affect reproduction. An especially disadvantageous recessive trait expressed in a homozygous recessive individual is likely to eliminate itself, naturally limiting the expression of its phenotype. Third, recessive deleterious alleles will be "masked" by heterozygosity, and so heterozygotes won't be selected against (assuming dominance).
Managing inbreeding depression
Introducing new genes from a different population can reverse inbreeding depression. Different populations have different deleterious traits, and therefore won't result in
homozygosity in most
loci in the offspring. This is known as
outbreeding enhancement, practiced by conservation managers and zoo captive breeders to prevent homozygosity. However, intermixing two different populations may give rise to unfit polygenic traits in
outbreeding depression
Example taxa subject to inbreeding depression
Example taxa not subject to significant inbreeding depression
despite extremely low effective population sizes
Chatham Islands Robin
Laysan Duck (data equivocal; severe population fluctuations probably natural)
Mauritius Kestrel
Nihoa Carnation
Thai Ridgeback, a dog breed
ToromiroFurther Information
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