heterosis

heterosis (hĕt'ərō`sĭs): see hybrid.

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heterosis

 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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heterosis [‚hed·ə′rō·səs]

(genetics)

The increase in size, yield, and performance found in some hybrid plants and aninals, especially if the parents are from inbred stocks. Also known as hybrid vigor.

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Heterosis

Hybrid vigor or increase in size, yield, and performance found in hybrids, especially if the parents have previously been inbred. The application of heterosis has been one of the most important contributions of genetics to scientific agriculture in providing hybrid corn, and vigorous, high-yielding hybrids in other plants and in livestock. See Breeding (animal), Breeding (plant) See Genetics, Mendelism

There are two principal hypotheses to account for the association of size and vigor with heterozygosity, dominance and overdominance. The dominance hypothesis notes that any noninbred population carries a number of recessive genes that are harmful to a greater or lesser extent, but which are rendered ineffective by their dominant alleles. As they become homozygous through inbreeding, they exert their harmful effect. With hybridization, some of the detrimental recessives contributed to the hybrid by one parent are masked by dominant alleles from the other, and an increase in vigor is the result. The alternative hypothesis is that there are loci at which the heterozygote is superior in vigor to either homozygote. This, the overdominance hypothesis, also has the consequence that vigor is proportional to heterozygosity. The dominance hypothesis has been more widely accepted, but the two are very difficult to distinguish experimentally, and it is likely that overdominant loci are playing an appreciable role in heterosis, particularly in determining why one hybrid is better than another. See Dominance