A statistical model was developed to determine the likelihood of a twin kinship, that is, the offspring of a pair of monozygotic or dizygotic twins under three types of inheritance: sporadic, single locus fetal genetic, and single locus maternal genetic. Samples of 8,000 kinships were simulated for a discrete trait under various hypotheses, and the likelihood determined for each type of etiology. The results indicated that the pedigree analysis procedures formulated here could efficiently detect sporadic or single locus effects with a power approaching 100%, although the parameter estimates obtained were slightly biased. Further analyses revealed that the type of pedigree analysis formulated in this study was found to have equivalent power for equal or unequal frequencies of kinships by the sex and zygosity of the twin parent. It was suggested that further studies be carried out that included the twins and spouses in the likelihood equations, as well as tests of more sophisticated models.
