AN IMPROVED MULTIPOINT SIB-PAIR ANALYSIS OF QUANTITATIVE TRAITS

Kruglyak and Lander (1995) recently published a multipoint sib-pair pr ocedure based on the expected distribution of zero, one and two marker alleles shared identical by descent (ibd) and the method of maximum-l ikelihood (ML). Their approach uses phenotypic sib-pair differences, w hich ignores the bivariate structure of sib-pair data. Their simulatio ns suggested that their method was more powerful than the regression m ethod of Haseman and Elston (1972). We show through computation and si mulation that their approach can be made more powerful still if the bi variate nature of sib-pair data is acknowledged. In addition, methods based on the average number of shared alleles that also employ bivaria te ML procedures (Nance and Neale, 1989; Xu and Atchley, 1995) are mor e powerful than the approach they recommend and very similar to true M L using the distribution of ibd. The simple ML approach using the aver age number of shared alleles that we recommend seems to offer both opt imal power and flexibility.