Folic acid and chromosome breakage. III. Types and frequencies of spontaneous chromosome aberrations in proliferating lymphocytes.

The types and frequencies of spontaneous chromosome aberrations were studied in human lymphocytes cultured for 96 h in minimal essential medium (MEM) or MEM without folic acid (MEM-FA). In both media, the most frequent aberrations were chromatid gaps, isochromatid gaps and chromatid breaks. Chromosome (isochromatid) breaks and dicentrics were seen less frequently. Neither of these less frequent aberrations was seen in 4000 cells from MEM, but both were seen in 4000 cells from MEM-FA.