From: A comparison of discrete versus continuous environment in a variance components-based linkage analysis of the COGA data
Subject i smokes
Subject j smokes
Covariance Matrix
1
Ω = 2 Φ σ2xg + I σ2xe
0
Ω = 2 Φ σ2yg + I σ2ye
Ω = 2 Φ σxg σyg ρg + I σxe σye