Specificity of daunomycin in causing chromosome aberrations in human leukocytes

When the chromosome aberrations induced in human leukocytes in culture with daunomycin (Dm) (0.015 g/ml, with or without added arginine) are analyzed with respect to sites of breakage and reunion, non-randomness is observed, both between and within chromosomes. These results suggest either a site-specificity of action of the drug or site-specific sensitivity or both. Superficially, the data give an indication of the phenomenon of somatic crossing-over having occurred. However, if chromosome breakage and reunions of broken ends are considered as two events, independent of each other, the frequency of exchanges between homologues and apparent homologues is lower than the expected frequency in cases of groups involving chromosomes 6–12/X and 13/15 and almost equal to the expected frequency in cases of chromosomes 1, 2 and 3.