Analysis of X-chromosome inactivation patterns. Amplification of the CAG repeat polymorphism at the HUMARA locus either without (−) or with (+) prior Hpa II digestion. Lanes 1 and 2, the mother of patient HO (I-1); lanes 3 through 6, the 2 sisters of patient HO (II-1 in lanes 3 and 4; II-4 in lanes 5 and 6). Note the completely skewed pattern in the carrier (lane 4), the random pattern in the normal sister (lane 6), and the incompletely skewed pattern in the mother (lane 2).