As distribuições intercromossômicas de pontos de quebra vindos de aberrações tipo cromátide induzidas por raios gama em células de ovário de hamster chinês foram analisadas. Na maioria dos cromossomos a distribuição foi a esperada de comprimentos de cromossomos para quebras simples ou, em caso de trocas, o respectivo comprimento corrigido. Em uns poucos cromossomos, houve desvios a partir do esperado para quebras de cromátides, trocas, trocas dentro do braço e trocas entre braços. Especialmente interessantes foram os resultados relativos aos cromossomos 2 e 8, que se envolveram nas trocas mais freqüentemente do que o esperado. Um "fenótipo de troca" para esses cromossomos é proposto e possíveis explicações para a distribuição não-aleatória de pontos de quebra cromossômicas são apresentadas.

Interchromosomal distributions of breakpoints from chromatid-type aberrations induced by gamma rays in Chinese hamster ovary (CHO) cells were analyzed. In most chromosomes the distribution was as expected from chromosome lengths for simple breaks or the respective relative corrected length in case of exchanges. There were deviations from expectation in a few chromosomes for chromatid breaks, interchanges, intra-arm intrachanges and inter-arm intrachanges. Especially interesting are the results concerning chromosomes 2 and 8, which were more often involved in exchanges than expected. An "exchange phenotype" for these chromosomes is proposed and possible explanations for the nonrandom distribution of chromosome breakpoints are presented.

Chromatid gaps and breaks induced by the restriction endonucleases AluI and BamHI in the long arm of chromosome 1 of Chinese hamster ovary cells were microphotometrically scanned and mapped to a quantitative G-band map. More than 50% of chromatid breaks appeared as chromatin losses of greater than 5% of the total arm length. The majority of chromatid gaps and breaks as well as chromatin losses induced by both restriction endonucleases were non-randomly located in a region from 0.35 to 0.65 relative length units of the long arm of chromosome 1. We suggest that the access of these endonucleases to chromosomal DNA depends on the local organization of the chromatin.