Cytochemical Differentiation along Human Chromosomes

THE binding of fluorescent substances to well defined chromosomal regions has been demonstrated in plant and animal materials by Caspersson and his collaborators, and this taken as evidence for chemical differentiation along the chromosomes1,2. Quinacrine mustard (QM), an alkylating fluorochrome, binds very specifically to the heterochromatic areas or regions of the M chromosome of Vicia faba1,2. Alkylating agents are thought to interact with G·C-rich areas in DNA by alkylation of guanine3,4, and it was suggested that binding of such agents to chromosomal regions might indicate G·C-rich areas in them1,2. The specificity and reproducibility of these techniques in Vicia prompted me to explore their use with human chromosomes, possibly to identify individual chromosomes.