Simulation of a common oligogenic disease with quantitative risk factors. GAW9 problem 2: the answers

For Problem 2, simulated family data were provided for a common oligogenic disease that was defined by imposing a threshold, T, on a quantitative trait, Q1. Every individual with a value of Q1 > T (where T = 87.5) was defined as affected. Participants were told that three other quantitative traits (Q2, Q3, and Q4) and an environmental factor (EF) also were thought to be associated with the disease as intervening variables, and that 12 candidate loci (C1 - C12) were postulated to influence traits associated with the disease. The tasks for GAW9 were to characterize the genetic and environmental contribution to Q1 (and the disease), Q2, Q3, and Q4, and to localize any single genes that had detectable effects.