Mating of closely related individuals.
The opposite is outbreeding, the mating of unrelated organisms. Inbreeding is useful in keeping desirable characteristics or eliminating undesirable ones, but it often results in decreased vigour, size, and fertility of the offspring because of the combined effect of harmful gene s that were recessive in both parents (see recessiveness ). The closest type of inbreeding is self-fertilization . In linebreeding, mates are selected on the basis of their relationships to a certain superior ancestor. The backcross (crossing a first-generation hybrid with one of the parental types) is a common method of inbreeding.