Q.Define heterosis.

Heterosis, or hybrid vigour, is the superiority of an F1 hybrid over its two parents in one or more traits, arising from the combination of favourable dominant alleles (or heterozygote advantage) contributed by genetically distinct parents.

Explanation

Heterosis is the phenomenon in which crossing two genetically dissimilar (often homozygous, inbred) parental varieties or lines produces an F1 hybrid offspring that displays greater vigour — such as increased size, yield, growth rate, or resistance to disease — than either of its parents. Heterosis is widely exploited commercially in plant and animal breeding programmes to produce high-yielding hybrid varieties (e.g. hybrid maize, hybrid vegetables). However, this hybrid vigour is generally not maintained in subsequent generations (F2 onwards), since the favourable heterozyg …