Q.74
Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : In a crossbreeding experiment, the Hybrid vigour /heterosis is observed
Reason (R) : The hetrosis is observed in first generation is subsequently halved in the second generation
In light of the above statements, choose the most appropriate answer from the options given below
- Assertion (A) is Correct: Hybrid vigor (heterosis) refers to the superior phenotypic performance of crossbred progeny ($F_1$) compared to the average of their purebred parental breeds (mid-parent value), widely exploited in livestock crossbreeding schemes (e.g., Karan Swiss, Karan Fries).
- Reason (R) is Correct: In the $F_2$ generation produced by mating $F_1 \times F_1$, segregation and recombination break up non-additive favorable allelic interactions (dominance and epistatic complexes), leading to heterosis breakdown where individual heterosis is halved:
- Relationship: While both statements are scientifically sound, (R) describes the genetic breakdown of heterosis in segregating $F_2$ generations rather than providing the physiological or genetic mechanism behind the expression of $F_1$ hybrid vigor (which arises from dominance, overdominance, and epistasis).
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