The spontaneous frequency of chromosomal aberrations and sister-chromatid exchanges in cultured peripheral lymphocytes of a single blood donor sampled more than 200 times.

Blood samples were taken from a single individual over 200 times during a 12-year period and the lymphocytes cultured with the intention of examining the frequencies of chromosomal aberrations and sister-chromatid exchanges (SCE). The data presented here are a compilation of the aberration frequencies in untreated control cultures from all experiments in which at least 100 metaphases were analysed for chromosomal aberrations (135 experiments), and at least 25 for the frequency of SCE (24 experiments). Since 52-h cultures displayed a high mitotic index and a low percentage of second-division metaphases (7%), this culture time was chosen for 70 experiments investigating the frequency of chromosomal aberrations. The inter-experimental variation in aberration frequency was found to be small, 0-4 aberrations per 100 cells, with a mean of 0.79 +/- 0.94. The fact that the spontaneous frequency of chromosomal aberrations was distributed according to the Poisson expectation indicates that the mean aberration frequency for a single subject is constant over time. On average, 80% of the aberrations were chromatid breaks (0.59 aberrations per 100 cells). Isochromatid breaks (or chromosome deletions) were not uncommon (0.11). Chromatid exchanges (0.03), as well as dicentric (0.014) and ring (0.014) chromosomes were rare. The incidence of SCE was examined in lymphocytes grown for 72 h in the presence of 20 microM 5-bromodeoxyuridine. The mean number of spontaneous SCE/cell was 6.41 +/- 0.69. The variation in SCE frequency between experiments was small, the coefficient of variation being only 0.11.