Definitive Evidence for the Short Arm of the Y Chromosome associating with the X Chromosome during Meiosis in the Human Male

Abstract

MEIOTIC studies on the human male during the past thirty years, notably those of Koller¹ and Ford and Hamerton², have shown that the X and Y chromosomes associate at meiotic prophase. Whether the chromosomes form a true chiasma or not has never been demonstrated convincingly. Because the position of the centromeres of the chromosomes cannot be identified with certainty in meiotic preparations, there has been much speculation as to whether it is the long or the short arms of the Y chromosome which associate with the X. Thus, Sasaki and Makino³ suggested that the X–Y chromosome association involved the short arms of the Y, and Hultén et al.⁴ suggested the long arms of the Y. The best cytological evidence has come from McIlree et al.⁵ on a male with a dicentric Y chromosome involving a presumptive deletion of the short arms. At diakinesis the dicentric Y chromosome did not associate with the X, and Jacobs therefore suggested that in normal circumstances the Y chromosome might have associated with the X by its short arms⁶. From phenotype–karyotype correlations, Ferguson-Smith^7,8 deduced that part of the long arms of the Y chromosome was homologous with part of the short arms of the X, and that this region was involved in the X–Y association. From the appearance of the X–Y association at diakinesis in testicular biopsies from a population of normal males, we have tentatively concluded that the short arms of the Y chromosome are involved in associating with the X chromosome.