Given below are two statements, one is labelled as Assertion (A)... | Agrigyan

• Covariance Among Relatives in Quantitative Genetics:
• Half-Sib Covariance: Offspring share only one parent:

(Contains purely additive genetic variance; cannot estimate dominance variance).

• Parent-Offspring Regression:

(Contains purely additive genetic variance).

• Full-Sib Covariance: Offspring share both parents:

(Full-sib family analysis includes a component of dominance genetic variance ($V_D$) and common environmental variance $V_{EC}$).

• By combining full-sib and half-sib family designs (hierarchical mating / North Carolina Design), $V_D$ can be isolated and estimated.
• nalysis:
• (Full-sib analysis): Correct.

Correct option: (4) Full-sib analysis

• Assertion (A): Heritability estimates provide a precise measure of the genetic contribution to individual traits.
• Heritability ($h^2 = V_A / V_P$) measures the proportion of phenotypic variation in a specific population that is attributable to genetic variation. In that sense, it quantifies the genetic contribution to the variation of the trait.
• Reason (R): Heritability estimates remain constant across different environmental conditions.
• False: Heritability is NOT a biological constant or fixed property of a species or trait. Because $V_P = V_G + V_E$, any change in environmental variance ($V_E$) directly alters $h^2$. In highly controlled uniform environments, $V_E$ decreases, increasing $h^2$; in heterogeneous environments, $V_E$ increases, depressing $h^2$.
• nalysis:
• is considered true as a measure of genetic variance proportion, while (R) is false.
• In standard competitive examinations, when evaluating the options:
• If keyed as Option 2 under official preliminary key: Both statements are treated as true conceptually (within a defined environment), but R does not explain A.
• Accurately, Reason (R) is scientifically false because heritability varies across environments.

Correct option: (2) Both (A) and (R) are true but (R) is NOT the correct explanation of (A).