Chromosome map of cosmid clones constructed with Chinese hamster genomic DNA.

By fluorescence in situ hybridization (FISH), we constructed a chromosome map of 324 site-specific clones and 119 painting clones, which were isolated from a cosmid library of Chinese hamster genomic DNA. The site-specific clones were distributed among all chromosomes except chromosome 10 and the Y chromosome. On the other hand, FISH signals of painting clones were mainly found in heterochromatic regions. First, the various combinations of clones painting centromeric regions suggest that the centromeric heterochromatin of Chinese hamster chromosomes is extremely diverse in its repetitive sequence composition. Second, the long arm of the X chromosome and the whole Y chromosome, both heterochromatic regions, were simultaneously painted by many clones. The pattern of co-localization indicated that a proximal segment of the long arm of the X chromosome matches the complete long arm of the Y chromosome, whereas a distal segment of the long arm of the X chromosome is comparable to the whole short arm of the Y chromosome. Thus, these findings suggest that the corresponding segments of the X and Y-chromosomes have common repeated DNA elements.