Taken from Ford et al. (1994). Data from 33 families, each containing at least 4 individuals with ovarian or breast cancer diagnosed before age 60, and each having a posterior probability of linkage to BRCA1 of at least 90%. The pink curve represents estimations of the overall penetrance of BRCA1 obtained by maximizing the LOD score with respect to different penetrance functions. This is equivalent to maximizing the likelihood of the marker data, conditional on all the disease phenotype data and allows the penetrance to be estimated free of bias due to ascertainment of families on the basis of multiple affected individuals. To determine the risk of contralateral breast cancer in women (blue curve), those with breast cancer diagnosed before age 60 were followed up. Age- specific frequency rates of contralateral breast cancer were estimated from the observed number of cases and person-years of follow-up. An estimate of breast cancer risk in carriers (yellow curve) was then obtained by doubling the observed incidence rates.