An autoradiographic study of the chromosomes of the rat,with special regard to the sex chromosomes

The pattern of terminal DNA synthesis of rat chromosomes was studied by means of tritiated thymidine incorporation and autoradiography. In the female, an entire X-chromosome underwent relative out-of-phase replication. In the male, the Y-chromosome showed a remarkable late replication. Several pairs of autosomes exhibited characteristic replicating patterns which were useful for their identification. The relation between the less prominent out-of-phase replication of the late replicating X-chromosome and the difficulty in finding the sex dimorphism of interphase nuclei of the rat is discussed.Contribution No 710 from the Zoological Institute, Faculty of Science, Hokkaido University, Sapporo.One of the authors, S. Makino, is much delighted to dedicate this paper to Professor Dr. J. Seiler in celebration of his 80th anniversary, on the 16th May, 1966.