Revolutionary Cytogenetics

Although the typical human being has 46 rather characteristic-appearing chromosomes, distinct variations in the size and shape of chromosomes may be present in apparently healthy persons.1 In spite of these individual variations, cytologists have successfully used the gross characteristics of chromosomes to analyze the karyotype, but this process has been relatively imprecise. The available methods permitted the organization of chromosomes into seven groups lettered A through G. Only in the A group could distinctions be made between every chromosome pair. In the other groups some distinctions were difficult, and others impossible. Autoradiography could distinguish the chromosomes in the B, D.