Genetic Variance Components: Additive, Dominance and Epistatic Variances, and ANOVA Partitioning - Fish Genetics and Breeding | 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

• Official Final Answer Key: The official NTA final answer key designated Option 2 (Epistatic genetic variance).
• Classical Quantitative Genetics Context: In quantitative genetics ($V_P = V_G + V_E + V_{GE}$), total phenotypic variance is partitioned into:
• Genetic Variance ($V_G$): Includes Additive genetic variance ($V_A$), Dominance genetic variance ($V_D$), and Epistatic/Interaction genetic variance ($V_I$).
• Environmental Variance ($V_E$): Reflects variance arising strictly from non-genetic external conditions (temperature, feed availability, density, water quality).
• Exam Strategy Note: While environmental variance is conceptually non-genetic, candidates should record Option 2 as the officially scored answer by NTA.

Correct option: (2) Epistatic genetic variance

• Statistical Partitioning of Quantitative Traits:
• Continuous quantitative traits (growth rate, body length, weight) are governed by polygenes and influenced by environmental variation.
• Analysis of Variance (ANOVA) is the fundamental statistical tool developed by R. A. Fisher to partition total phenotypic variance into component sources:
• Between-sire variance
• Between-dam within-sire variance
• Within-family (error) variance
• These variance components are directly used to calculate additive genetic variance ($V_A$) and estimate heritability ($h^2$).
• nalysis:
• (ANOVA): Correct.
• (Chi-square test): Used for discrete Mendelian ratios.
• (t-test): Compares two sample means.

Correct option: (4) ANOVA