Intraclass correlation coefficients among pairs of relatives were calculated using FCOR, a component of S.A.G.E. 4.2 [6] with pedigrees weighted equally. Heritability estimates for maximum number of cigarettes per day were obtained using the variance-components (VC) approach implemented in the SOLAR package 1.7.3 [7], which partitions the total phenotypic variance into additive genetic variance attributable to the QTL, residual polygenic additive genetic variance, and variance due to random environmental effects. Oligogenic joint linkage and segregation analysis was performed using Bayesian Markov chain Monte Carlo (MCMC) methods implemented in LOKI 2.2 [8], with sex and age as covariates.
