Segregation of a skewed pattern of X-chromosome inactivation. The autoradiograph shows the results of amplification of the HUMARA polymorphism either without (−) or with (+) prior digestion with HpaII. Each allele appears as a doublet. With reference to the family tree in Fig 1, the subjects analyzed are as follows: 1 =II:13 (mother of the patient); 2 = II:4 (father of the patient); 3 = III:2 (patient); 4 = III:4 (sister of the patient); 5 = III:5 (sister of the patient); 6 = IV:1 (daughter of the patient); 7 = IV:3 (daughter of the patient). Notice that 1, 3, and 7 show a skewed pattern of X-chromosome inactivation, 4 and 5 are random, and 6 is uninformative.