Previous longevity studies of related individuals such as twins or siblings based on the major gene model have shown that the frequency and the relative risk of mortality of a beneficial allele in the population could be estimated. If, in addition to survival data for related individuals, the genetic markers data are available, one could try to locate the longevity allele in the genome. In the case where the phenotypic trait is life span or age at onset of disease, a two-step procedure can be used. First, the parameters of bivariate survival functions must be estimated from bivariate survival data for twins without markers. The second step is focused on determining the position of longevity genes between respective markers. To calculate the joint distribution of inheritance vector and genetic markers, the hidden Markov chain technique is used. This approach is illustrated with a simulation example for one longevity gene.