1. The phenomenon that progeny of diverse varieties of a species or crosses between species exhibit greater biomass. speed of development, and fertility than both parents is termed as
(1) Dominance            (2) Over dominance
(3) Mid parental value  (4) Heterosis

Introduction:
Heterosis, also known as hybrid vigor, is a fascinating genetic phenomenon where the offspring resulting from crosses between diverse varieties of the same species or even between different species exhibit superior qualities compared to both parents. These enhanced traits can include increased biomass, faster development, and improved fertility. This biological advantage has significant implications in agriculture and breeding, providing more robust and productive hybrids.

Explanation of the Options:

1. Dominance:
   Dominance refers to a genetic situation where the dominant allele conceals the effect of a recessive allele at the same gene locus. In the context of hybrid offspring, the dominance hypothesis suggests that harmful recessive alleles present in the parents get masked by dominant alleles in the hybrid, resulting in better performance than either parent alone. However, dominance alone doesn’t always explain the superior performance seen in hybrids.

2. Overdominance:
   Overdominance is a genetics hypothesis where the heterozygous genotype at a particular locus produces a phenotype superior to either of the homozygous genotypes. This means that the hybrid’s heterozygote condition exceeds the traits of both homozygote parents, contributing to hybrid vigor. Overdominance explains the increased fitness and vigor in hybrids due to superiority at the heterozygous loci.

3. Mid Parental Value:
   Mid-parental value is the average of the parental traits. Sometimes offspring traits fall between the parents’ traits, showing an intermediate phenotype. It contrasts with heterosis, where the hybrid surpasses both parents.

4. Heterosis:
   Heterosis is the term used to describe the phenomenon where the progeny of crosses between genetically diverse parents exhibits greater biomass, faster developmental speed, and higher fertility than either parent. It encompasses the beneficial effects explained by dominance and overdominance and is widely exploited in plant and animal breeding for developing superior hybrids.

The correct answer to the question is (4) Heterosis.

This hybrid vigor phenomenon results in offspring that perform better than both parents thanks to genetic interactions like dominance and overdominance. Heterosis is crucial for breeders aiming to enhance crop yield, growth rate, and overall vigor.

References:

• Heterosis is described as the increased function and superior traits in hybrids compared to parents.

• Dominance and overdominance are genetic explanations for heterosis.

• Mid-parental value describes average parental traits, differing from heterosis.

This article covers the key concepts behind heterosis, enabling better understanding and application in genetics and breeding programs.