The determination of the chromosomal makeup of cells in man and in the experimental animal has acquired a new importance since the discovery of the sex chromatin body by Barr and Bertram in 1948.1 As so often happens in our times, one discovery followed another: in 1956 the exact number of chromosomes in man was shown to be 46,2,3 the Denver system for chromosomal classification according to size and the position of the centromere was internationally accepted, and evidence was provided that certain common congenital disorders are due to abnormalities of either the sex chromosomes (X,Y) or of the remaining 44 chromosomes or autosomes.
Recently, a further sophistication of the prior systems of chromosomal identification was introduced, namely chromosomal banding. It has been demonstrated that each one of the chromosomal pairs has a specific banding pattern that can be demonstrated by using either a fluorescent dye, quinacrine, as