The frequency and distribution of sister chromatid exchanges in human chromosomes

The distribution of sister chromatid exchanges (SCEs) both between and within chromosomes was studied in cultured human lymphocytes using the BRDU-Giemsa technique. In general, the distribution of SCEs between chromosomes was a function of chromosome length. However, chromosomes of the B group had more exchanges than expected on this basis, while the E, F, and G groups had less than expected. Analysis of cells showing both G-banding and sister chromatid differential staining indicates that the distribution of exchanges within the chromosomes is non-random and possible reasons for the observed distribution pattern are discussed.