Heterosis, or hybrid vigor or outbreeding enhancement, is the increased function of any biological quality in a hybrid offspring. It is the occurrence of a genetically superior offspring from mixing the genes of dissimilar parents. Heterosis is the opposite of inbreeding depression, which occurs in the offspring of closely related parents.
The term often causes controversy, particularly in regard to selective breeding of domestic animals, because sometimes it’s inaccurately claimed, that all crossbred plants or animals are genetically superior to their parents. It’s only true in certain circumstances. When a hybrid is seen to be superior to its parents, this is known as hybrid vigor. When the opposite happens, and a hybrid inherits traits from its parents that makes it unfit for survival, the result is referred to as outbreeding depression. Typical examples of this are crosses between wild and hatchery fish that have incompatible adaptations.
The Daily Omnivore 
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