Mammalian Cell Chromosome Counts : a Simple Method for making Preparations

FOR those who work with small mammals, it is sometimes desirable to determine the chromosome complement in cells of particular individuals. Until recently, the most reliable technique for chromosome number determinations depended on the reasonably high mitotic rate and other desirable properties of the seminiferous tubules (for example, Matthey 1 ). The difficulty with those techniques is that they do not permit the assessment of chromosome numbers in females, or in males apart from during the breeding season. Beatty 2 described a method of preparing corneal epithelial cells for chromosome counts, which overcame the shortcomings of relying on testicular cells, but many of the metaphase plates were not adequately spread. As a consequence, chromosome counts of only 20 cells from a total of 445 could be listed as exact counts. More recently, Ford et al. 3 and many other workers, have described very elegant techniques for mammalian chromosome counts, employing short-time culture of cells from a variety of tissues, primarily bone marrow. The primary difficulty with these techniques is the fact that very few laboratories have the equipment or personnel necessary for the carrying out of tissue culture. Another difficulty is the apparently large number of cells which possess chromosome numbers different from the diploid number. One cannot be sure if this heteroploidy is present in the tissue in the live animals or arises as a result of the extensive preparatory technique. This communication sets forth a relatively simple method for preparing corneal epithelium cells for reliable chromosome counts.