Human Heredity 21: 523-542 (1971) A General Model for the Genetic Analysis of Pedigree Datal R. C. ELSTON and J. STEWART Department of Biostatistics and the Genetics Curriculum, University of North Carolina, Chapel Hill, N.C., and Department of Genetics, Milton Road, Cambridge Abstract. Assuming random mating and random sampling of Key Words pedigrees, the likelihood of a set of pedigree data is developed in terms Pedigree data of: (1) the population distribution of the different genotypes; (2) the Genetic analysis phenotypic distributions for the different genotypes, and (3) the geno- typic distribution of offspring given the parents' genotypes. This last is given for any number of unlinked autosomal loci, two linked autosomal loci, an X-linked locus, and combinations of these possibilities. Methods are given for using this likelihood to test specific genetic hypotheses and for genetic counselling, I. Introduction The purpose of analysing pedigree data is to establish the presence or absence of a genetic mechanism for the manifestation of a particular trait or set of traits; to elucidate such a mechanism, if it is present; and to classify individuals for their genotypes. By pedigree data we mean data collected on one or more groups of related individuals, a group being more extensive than just parents and children (families): thus more than two generations will be involved. Whereas it is possible to examine genetic mechanisms without such data, using families, pairs of relatives, or even unrelated individuals, pedigree data provide the most genetic information. A typical pedigree may comprise a hundred or so individuals covering four or more generations, and from a genetic point of view such a group of individuals is capable of yielding far more information than can be obtained from the same number of individuals 1 This investigation was supported by a Public Health Service Research Career Develop- ment Award (1-K3-GM-31, 732), training grant (GM 00685) and research grant (GM HD 16697) from the National Institute of General Medical Sciences. I I