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The term heterosis often causes confusion and even controversy, particularly in selective breeding of domestic animals, because it is sometimes (incorrectly) claimed that all crossbred plants and animals are "genetically superior" to their parents, due to heterosis, [citation needed]. but two problems exist with this claim:
Inbreeding is also used to reveal deleterious recessive alleles, which can then be eliminated through assortative breeding or through culling. In plant breeding, inbred lines are used as stocks for the creation of hybrid lines to make use of the effects of heterosis. Inbreeding in plants also occurs naturally in the form of self-pollination.
The divergence between the (two) parent lines promotes improved growth and yield characteristics in offspring through the phenomenon of heterosis ("hybrid vigour" or "combining ability"). Two populations of breeding stock with desired characteristics are subjected to inbreeding until the homozygosity of the population exceeds a certain level ...
Wright introduced the inbreeding coefficient F as the correlation between uniting gametes in 1922, and most of the subsequent theory of inbreeding has been developed from his work. The definition of the inbreeding coefficient now most widely used is mathematically equivalent to that of Wright. [7]
One of the most ancient types of hybrid animal is the mule, a cross between a female horse and a male donkey. The liger is a hybrid cross between a male lion and female tiger. The yattle is a cross between a cow and a yak. Other crosses include the tigon (between a male tiger and female lion) and yakalo (between a yak and an American bison).
A mule is a sterile hybrid of a male donkey and a female horse.Mules are smaller than horses but stronger than donkeys, making them useful as pack animals.. In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different varieties, subspecies, species or genera through sexual reproduction.
However animals often do not avoid inbreeding. [7] Among animals, inbreeding avoidance is highly variable. [8] Inbreeding avoidance through mate selection appears to evolve only when there is both a risk of inbreeding depression and there also are frequent encounters between potential sexual partners that are related to each other. [8]
The offspring produced as a result of breeding animals of one breed with other animals of another breed are known as crossbreeds or mixed breeds. Crosses between animal or plant variants above the level of breed/cultivar (i.e. between species, subspecies, botanical variety, even different genera) are referred to as hybrids. [6]