Abstract
Asynchronous centromere division, i.e., variation in the distance between sister centromeres in the same cell, has been observed in bone-marrow cells of the Chinese hamster (2n = 22). The cells were harvested with brief hypotonic treatment but without colchicine. In each of 20 cells, the chromosomes were arranged in a sequence according to decreasing intercentromeric distance, i.e., the distance between sister centromeres. The 20 sequences exhibited a significant degree of concordance, permitting the construction of a best-estimate or overall sequence. There appears to be the same sequence among the chromosomes of each haploid set, although the two homologs of each pair ranked, on the average, 7.6 positions apart. The data on the X and Y chromosomes, which are morphologically distinguishable, indicate that the intercentromeric distance of the X is significantly larger than that of the Y. The concordance could be either an artifact of the harvest procedure (hypotonic treatment, flattening, etc.) or a result of the chromosomes dividing in a sequence at the onset of anaphase. These alternatives are discussed along with the relation of the findings to such chromosome characteristics as length and the time of DNA replication.