Exploiting Maximum Heterosis
Type of cross breeding which exploites 100% maternal, paternal as well as individual heterosis-
- Four breed crosses
- Double two breed crosses
- Rotational crossing
- Both a & b — Correct Answer
Explanation:
Correct Answer: Both a & b (Four-breed cross AND Double two-breed cross)
A Four-breed cross (also called a Double two-breed cross) is the crossing system that exploits 100% maternal, paternal, and individual heterosis simultaneously by using four genetically distinct breeds across two generations of crossing.
Heterosis in Cross Breeding Systems
| Crossing System | Individual Heterosis | Maternal Heterosis | Paternal Heterosis |
|---|---|---|---|
| Two-breed cross (A × B) | 100% | 0% | 0% |
| Three-breed cross (C × AB♀) | 100% | 100% | 0% |
| Four-breed / Double two-breed (CD♂ × AB♀) | 100% | 100% | 100% |
| Rotational crossing | ~67% | ~67% | Varies |
Heterosis — Key Facts
- Heterosis depends on extent of heterozygosity and Non-additive gene action (Dominance, Over-dominance, Epistasis)
- Traits with low heritability (h²) show high degree of heterosis and vice versa
- Maximum hybrid vigour is obtained in F1 generation
- Heterozygosity reduces by 50% each generation → heterosis also reduces
- Term "Heterosis/Hybrid Vigour" given by G.H. Shull
Why Other Options Are Wrong
- Four-breed cross alone → correct in itself; but so is Double two-breed cross (they are the same concept)
- Double two-breed cross alone → same reasoning as above
- Rotational crossing → achieves only ~67% heterosis, not 100% for all three components
📚 About this Topic — Animal Genetics & Breeding
This multiple choice question is from Animal Genetics & Breeding, Animal Refresher. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Genetics & Breeding to strengthen your preparation.
