Distribution of radiation-induced exchange aberrations in human chromosomes 1, 2 and 4

Purpose: To examine the distribution of radiation-induced breakpoints in ch romosomes 1, 2 and 4 both in relation to their DNA content and by localizat ion of the breaks along each chromosome. Material and methods: The work consisted of two studies, one with chromosom al aberrations found in persons after accidental exposure in Estonia in 199 4 and another involving aberrations seen in in vitro-irradiated lymphocytes . Localization of breakpoints in painted chromosomes involved in complete e xchange-type aberrations was conducted by applying a computerized measuring system on stored image-files. Results and conclusions: The yield of exchanges in chromosomes 1, 2 and 4 i n both studies was equal to that expected from their DNA content. In contra st, the breakpoint location of complete exchanges within these chromosomes was not random. Chromosomes 1 and 4 contained more breaks in the middle par ts of the p and q arms, whereas breaks were observed more uniformly along c hromosome 2. Complete exchanges, however, were very rare in the terminal re gions of all three chromosomes, most probably resulting from limitations in the resolution of small painted pieces.