NUMBERS of CHROMOSOMES in HUMAN LEUCOCYTES EXPOSED to ECDYSTERONE

All chromosomes could not be identified with certainty until relatively recently even with radiolabeling. Differential patterns in staining heterochromatin were then obtained by Gall and Pardue (1971) and others (Gagne et al., 191). In addition, Caspersson and colleagues (Caspersson and Zech, 1972) and others have used fluorescent banding that appears with ultra-violet illumination of chromosomes stained with quinacrine mustard to characterize each chromosome uniquely. This has clarified quickly some confusion in karyotyping syndromes of clinical significance. For example, trisomic chromosome 21 (newer terminology) in Down’s disease proved to be distinct from the Philadelphia chromosome now known to be chromosome 22 with a portion deleted. Previously the postulate that the same chromosome was involved in both abnormalities was attractive, since both are associated with neoplastic disease. Quinacrine mustard was selected on the basis of the supposition that it would bind to one of the nitrogen atoms in the guanine base of the nucleotide (Casperson et al., 1967). However, the bands that fluoresce do not correspond to the distribution of DNA determined spectrophotometrically, and the reason for differential regional affinity is not entirely clear at the present time.