The ordered arrangement of chromosomes in the Chinese hamster spermatocyte nucleus.

The question of chromosome distribution in the mammalian nucleus is addressed, and data are provided in support of the ordered arrangement of chromosomes in the Chinese hamster spermatocyte. Testicular cells were dispersed and air-dried without prior fixation, then stained and karyotyped. The position of chromosome telomeres in 217 pachytene spermatocytes was determined in relation to four concentric rings which equally divided the nuclear area. The distribution of telomeres showed a progressive decline from the central to the peripheral rings. This was particularly pronounced for chromosomes 1-7, but was reversed for the XY chromosomes. The distribution of the total as well as of the individual chromosomes was significantly different from that expected on the basis of random distribution. The only exceptions to this were chromosomes 8-10, which exhibited random distribution. Thus, while chromosomes 1-7 had a central position, the XY pair had a peripheral localization. The mean ring position appeared to be related to chromosome length, except for the XY chromosomes, suggesting that chromosome length may determine chromosome position.