Narrow Sense vs. Broad Sense Heritability

Correct Answer: Always less than or equal to broad sense heritability

From Table 12 in the notes:

• Narrow sense heritability (h²N) = VA / VP — only additive genetic variance in numerator
• Broad sense heritability (H²B) = VG / VP — total genotypic variance (VA + VD + VI) in numerator

Why Narrow ≤ Broad?

VG = VA + VD + VI, so VG ≥ VA always. Therefore VG/VP ≥ VA/VP, which means H²B ≥ h²N. They are equal ONLY when VD = 0 and VI = 0 (i.e., only additive gene action exists — no dominance, no epistasis).

Example (from notes, Q186)

If VA = 20, VG = 30, VP = 100: h²N = 20/100 = 0.20; H²B = 30/100 = 0.30. Narrow (0.20) < Broad (0.30) ✔