INACTIVATION CENTERS IN THE HUMAN X-CHROMOSOME

Abstract

Reported cases with a structurally abnormal X chromosome were compiled. These included 17 balanced and 26 unbalanced X-autosome translocations, each with inactivation of either a derivative X or a derivative of any of the autosomes. A further 52 cases with various structural rearrangements were studied. The shortest late-replicating segment in each arm was pter .fwdarw. p21 and q13 .fwdarw. qter. In both cases, they were detected in all or most metaphases, thus making the results convincing. In 1 case, the distal part of Xq,q25 or 26 .fwdarw. qter was probably inactivated in a small proportion of the cells. Apparently the former 2 segments and probably also the 3rd include an inactivation center(s). In a male with a 46,Y,dup(X)(q13q22), no part of dup X replicated late although it contained extra chromosome material.