of male drinking patterns was higher in those whose parent were frequent drinkers than in those from non/low drinking households (Cleveland and Wiebe 2003). Moreover, heritability of intoxication frequency was found to be more heritable in independent twins than in dependent twins in both adolescence and early adulthood (Penninkilampi-Kerola et al. 2005), In studies of adult alcohol phenotypes, Heath et al. (Heath et al. 1989) showed that the heritability of levels of alcohol consumption were around 0.50 for married women, but increased to 0.76 for unmarried women. Frequency of use was found to be more heritable in twins who displayed greater independence from their co-twin (vs. those who were dependent on their co-twin) (Penninkilampi-Kerola et al. 2005).
