Genetic Covariance Components in Relatives
Genetic covariance between Parent-offspring, half sibs, full sibs are respectively-
- $\frac{1}{2}V_{A}$, $\frac{1}{4}V_{A}$, $\frac{1}{2}V_{A} + \frac{1}{4}V_{D} + V_{EC}$ — Correct Answer
- $\frac{1}{2}V_{A}$, $V_{A}$, $\frac{1}{2}V_{A} + \frac{1}{2}V_{D} + V_{EC}$
- $\frac{1}{2}V_{A}$, $\frac{1}{2}V_{A}$, $\frac{1}{2}V_{A} + \frac{1}{4}V_{D} + V_{EC}$
- $\frac{1}{2}V_{A}$, $\frac{1}{4}V_{A}$, $\frac{1}{2}V_{A} + V_{D} + V_{EC}$
Explanation:
Correct Answer: ½VA, ¼VA, ½VA + ¼VD + VEC
The genetic covariance between relatives determines how much additive (and other) genetic variance they share in common — the basis of heritability estimation.
Covariance of Relatives — Summary Table
| Relative Pair | Genetic Covariance | h² Estimation Formula |
|---|---|---|
| Offspring & One parent | ½VA | h² = 2b (b = regression coefficient) |
| Offspring & Mid-parent | ½VA | h² = b |
| Half sibs | ¼VA | h² = 4t (t = intraclass correlation) |
| Full sibs | ½VA + ¼VD + VEC | h² = 2t (overestimates due to VD and VEC) |
Why Full-Sib Estimate is Unreliable
- Full sibs share not only ½VA (additive) but also ¼VD (dominance variance) and VEC (common environmental variance — shared womb, same dam, same early environment).
- This inflation of the covariance means the full-sib method overestimates h² — it is the least reliable method.
- Half-sib method is the best because paternal half-sibs share only ¼VA and are usually reared by different dams, minimizing VEC bias.
📚 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.
