Breeding of Vegetable, Spice and Tuber crops (2+1)

Theories of heterosis

• The term heterosis was first used by Shull in 1914.
• Heterosis is often called true heterosis or euheterosis.
• Heterosis may be defined as the superiority of an F1 hybrid over either its parents in terms of yield or some other character.
• Heterosis or euheterosis is classified as mutational and balanced heterosis.
• Mutational heterosis results from dominance gene action, i.e., masking of the deleterious effects of recessive mutant alleles by their dominant counterparts.
• Balanced heterosis, on the other hand, arises due to over-domianace gene action, i.e. superiority of the heterogygote over both the corresponding homozygotes.

Causes – Basis of Heterosis

• Various basis or causes of heterosis can be listed as follows
• Genetic basis
• Dominance hypothesis
• Overdominance hypothesis
• Epistasis
• Physiological basis
• Cytoplasmic basis
• Biochemical basis