• Full-Sib Correlation and Heritability:
• In quantitative genetics, full-sibs share half of their additive genetic variance and a quarter of their dominance genetic variance:

$$\text{Cov}(\text{FS}) = \frac{1}{2}V_A + \frac{1}{4}V_D + V_{EC}$$

• In an idealized population where non-additive genetic variance and common environmental variance are negligible, the intraclass correlation between full-sibs ($t$ or $r_{FS}$) is:

$$r_{FS} = \frac{\frac{1}{2}V_A}{V_P} = \frac{1}{2}h^2$$

• Rearranging to solve for narrow-sense heritability ($h^2$):

$$h^2 = 2 \times r_{FS} = 2 \times 0.25 = 0.50$$

• Conclusion: The heritability of this trait is 0.50 (Option 3).

Correct option: (3) 0.50