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recreating page from a serious perspective
'''Inbreeding''' is the practice of mating closely related animals. How close? So close, that among human beings the relations would be considered [[incest]]. For breeders, the practice has some advantages and disadvantages.<ref>Sarah Hartwell wrote, "Deleterious genes become widespread and the breed loses vigor." [http://www.dogbreedinfo.com/inbreeding.htm]</ref>
'''Inbreeding''' is breeding between closely related individuals in a population. In humans, close inbreeding is referred to as [[incest]].
== Mathematical definition ==
In [[population genetics]], the ''coefficient of inbreeding'' <math>F</math> is the probability that two alleles at a randomly chosen [[locus]] in an individual are identical by descent, meaning they are identical as a result of having come from a common ancestor. This number is normalized relative to a "base population" in which no alleles are assumed to be related. <math>F</math> is generally larger when more inbreeding occurs, such as in structured populations or small populations. In this way, inbreeding is related to [[genetic drift]].
== Inbreeding depression ==
Because inbreeding increases the [[Homozygous|homozygosity]] in a population, it can lead to the expression of [[recessive]] [[mutation]]s; since vastly more mutations are deleterious (harmful) than beneficial, this usually manifests as a genetic disorder, reducing the [[fitness]] of individuals.
For example, if an organism has a recessive, deleterious mutation and gives rise to many offspring, some of whom also carry this mutation, and some of those offspring mate, it is likely that they will produce some children who are homozygous for this recessive, deleterious [[allele]].
Inbreeding can thus cause homozygosity for deleterious alleles to become prevalent in a population, which reduces the overall population fitness.
On the other hand, if there are no deleterious alleles and the mutation rate is low, inbreeding is not necessarily harmful to the population. For example, [[creationism|creationists]] argue that, since [[Adam]] and [[Eve]] were created perfect and mutation rates were lower before the [[Flood]], marriage and breeding between Adam and Eve's descendants was not harmful or immoral in the way it is today.
== Inbreeding in animals ==
Breeding closely related animals allows a breeder to select desired traits and create a population where every individual has those traits. However, sometimes deleterious traits also "hitchhike" along with the desired traits as a result of inbreeding. This can lead to inbreeding depression.<ref>Sarah Hartwell wrote, "Deleterious genes become widespread and the breed loses vigor." [http://www.dogbreedinfo.com/inbreeding.htm]</ref> As an example, [[Pug]]s are a dog breed which has been bred for thousands of years, but genetic disorders relating to the eyes are common in the breed. [[Manx]] cats, known for having short tails, arose naturally due to [[genetic drift]], but problems such as spina bifida are very common.
One way to overcome inbreeding depression is by periodically introducing new genetic variation in a process known as outcrossing, where members of the breed are mated with individuals from outside the breed. This decreases the "purity" of the line, but can reduce the prevalence of genetic disorders.
== Notes ==
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