ONCE it was demonstrated that modification of methods applied to botanical material could be used successfully in mammalian cytogenetics,1 human cytogenetics began its explosive growth. By means of standard staining techniques for chromosomes, the correct diploid chromosome number for man was quickly established, and a number of human disorders were found to be caused by numerical or structural abnormalities. These findings and the growth of human cytogenetics depended essentially on the concatenation of two laboratory contributions. The first of these was the development of a method that made metaphase chromosomes easily available from the dividing cell.1,2 A necessary second development was that of cell culture. Once considered an exotic procedure, it has been brought to the point where its application is only slightly more problematic than standard microbiological culture procedures.
By the middle of the decade 1960-1970, more than 25 disorders had been catalogued as having their etiology