heterosis

/het'euh roh"sis/, n. Genetics.

the increase in growth, size, fecundity, function, yield, or other characters in hybrids over those of the parents. Also called hybrid vigor.

[1910-15; < LGk hetérosis an alteration. See HETERO-, -SIS]

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or hybrid vigor

Increase in such characteristics as size, growth rate, fertility, and yield of a hybrid organism over those of its parents.

Plant and animal breeders exploit heterosis by mating two different purebred lines that have desirable traits. The first-generation offspring generally show, in greater measure, the desired characteristics of both parents. Since this vigour may decrease if the hybrids are actually mated together, the parental lines must be maintained and crossed for each new crop or group desired.

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▪ genetics

also called  hybrid vigour 

      the increase in such characteristics as size, growth rate, fertility, and yield of a hybrid organism over those of its parents. Plant and animal breeders exploit heterosis by mating two different pure-bred lines that have certain desirable traits. The first-generation offspring generally show, in greater measure, the desired characteristics of both parents. This vigour may decrease, however, if the hybrids are mated together; so the parental lines must be maintained and crossed for each new crop or group desired.

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