Step 1: Understanding the Concept:
Heterosis, or Hybrid Vigour, is the phenomenon where the progeny (hybrid) of two genetically diverse parents shows superior performance compared to either parent.
This superiority can be in terms of yield, growth rate, resistance to pests, or environmental adaptability.
It is the biological driving force behind the global hybrid seed industry, particularly in crops like maize, sorghum, and pearl millet.
Step 2: Detailed Explanation:
The scientific understanding of heterosis evolved through various researchers:
1. G.H. Shull (1914): George Harrison Shull, an American geneticist, was working on inbreeding and cross-breeding in maize. He observed that while inbreeding led to a decline in vigor, crossing the inbred lines resulted in offspring that were significantly more productive. In a lecture in 1914, he proposed the term "heterosis" (from the Greek {heteros}, meaning 'different', and {osis}, meaning 'condition'). He suggested it as a more concise term for the physiological stimulus resulting from the "heterozygous" state. Thus, Shull is the person who coined the term.
2. Evaluation of other options:
- Bruce (1910): Proposed the Dominance Hypothesis, which suggests that heterosis results from the masking of harmful recessive alleles by dominant ones.
- East (1908): E.M. East was another pioneer in hybrid maize research alongside Shull, but he did not coin the specific term "heterosis."
- Hull (1945): F.H. Hull proposed the Overdominance Hypothesis, suggesting that the heterozygote (\(Aa\)) is superior to both homozygotes (\(AA\) and \(aa\)).
Step 3: Final Answer:
The term heterosis was coined by G.H. Shull in 1914 to describe the increased vigor of hybrids.
Therefore, the correct option is (D).