PARENTAL ORIGIN OF THE EXTRA CHROMOSOMES IN POLYSOMY-X

Five polymorphic index markers were analyzed by polymerase chain react ion (PCR) to ascertain the parental origin of the extra X chromosomes in seven polysomic cases (one 49,XXXXX, three 49,XXXXY, two 48,XXXY, a nd one 48, XXYY). All four X chromosomes in 49, X polysomies were mate rnal in origin and the extra X chromosomes in 48 X polysomies were pat ernal. In each case the multiple X chromosomes were contributed by a s ingle parent. Taken together with previously reported cases, these dat a support a single mechanism of sequential nondisjunction during eithe r maternal or paternal gametogenesis as the cause of higher order sex chromosome polysomy.