Fluorescent staining of human chromosomes.

Abstract

In the mid-1950's, Tjio and Levan applied the technics of plant cytology to the study of human cells and were able to demonstrate for the first time that 46 chromosomes were present in the normal human cell. This technical feat was followed in 1959 by the discovery that Down's syndrome was the result of an extra chromosome. The next technical advance resulted from the observation, in 1960, that kidney-bean extract ("phytohemagglutinin") contained a mitogenic substance that could stimulate peripheral leukocytes to divide. (The name phytohemagglutinin emphasizes the accidental origin of the extract's use as a mitogenic agent; the bean extract . . .