less than 10−4 (i.e., resulting in 99.99% zygosity certainty) (Nyholt, 2006). Additionally, most pairs were genotyped, as part of ongoing linkage studies, at a minimum of 20 (maximum of 1369) microsatellite markers. Only 16 pairs had fewer than 20 markers for one or both co-twins and consequently have not had zygosity confirmed through microsatellite genotyping. Of these, 6 pairs have been checked for blood group.
