The background to the determination of the human chromosome number

Abstract

THE DETERMINATION of the correct chromosome number in man was a direct consequence of the improvements in handling of mammalian chromosomes that came into use during the early 1950’s. These improvements were mainly applications of procedures developed much earlier in plant cytogenetics, for instance, squash methods with simultaneous fixation and staining of the chromosomes. They were based on Belling’s’ acetocarmine method of 1921, with the more selective stain orcein substituted for the carmine by La Cour” in 194 1. The first mammalian material that responded favorably to the acetic orcein squash technique was ascites tumors, in which the first karyotype analyses were made in 195 1 independently by Makinos in rat tumors and by Hauschka and Levan3 in mouse tumors. This technique gained general applicability in mammals after it had been adapted to cells to tissue culture. Two technical procedures, pretreatment with colchicine and hypot.onic swelling of the cells, made this possible. The action of colchicine on mitosis and chromosomes, the so-called c-mitosis, was described in Allium cells by the Gavaudans.’ in 1937, and by me,* in 1938; the hypotonic treatment technique was worked out independentlyby Hsu” and Hughes5 in 1952. The combination of these techniques was made in the laboratory of Dr. John J. Biesele at the SloanKettering Institute in New York, where 1 was a guest worker during the summer of 1955. One of my aims during my stay there was to try to obtain good chromosomes in mammalian tissue culture material. According to my laboratory record, 1 received cells on June 22 of a