Inbreeding is breeding between closely related individuals in a
population. In humans, close inbreeding is referred to as
incest. 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. As
an example, Pugs 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. In population genetics,