Analysis of inversions and sister chromatid exchanges in chromosome 3 of human lymphocytes exposed to X-rays

It has been shown repeatedly that exposure of G(1) cells unifilarily labell ed with 5-bromodeoxyuridine (BrdU) to X-rays leads to sister chromatid exch anges (SCE) when the cells are allowed to grow for one further cycle in the absence of BrdU. It has been suggested that damage induced by ionizing rad iation does not lead to 'true' SCE and that the observed SCE are 'false', r esulting from structural chromosomal aberrations, especially interstitial i nversions. We used a painting probe for the p14 region of human chromosome 3 and anti-BrdU antibodies to analyse the frequency of radiation-induced SC E in that chromosome. This method allowed us to discriminate between para- and pericentric 'true' and 'false' SCE. Our results indicate that most radi ation-induced SCE do not result from inversions.