A study of spontaneous mutations in human somatic cells is of interest from two points of view, at least. Primarily, the main problem is to understand the principles of somatic mutagenesis, and the fate of chromosome aberrations. Secondly, the somatic cells are used as models for the mutation process in human germ cells, which are experimentally more difficult at the present time.
There are a good many publications referring to the spontaneous mutation process in human somatic cells. Unfortunately, many of them are not consistent. Frequently the published data cannot be grouped owing to different approach in scoring chromosome aberrations, or because the data given in publications were not complete. These publications mostly referred to chromosome aberrations in leucocyte cultures and, to a lesser extent, in embryonic fibroblasts.
The literature analysis reveals that the majority of publications contains the data only on aberration frequency with no detailed analysis of their types and the distribution among the cells (Lubs and Samuelson, 1967;Sandberg, 1967;Jarvik and Kato, 1970). As a rule, the spontaneous chromosome aberrations were discussed with no relation to other factors. Only some publications touch the problem of sex and age influence (Court Brown et al., 1966 ; Boehkov et al., 1968Boehkov et al., , 1972)).
Accumulation of experimental data for the last years as well as improvement of techniques enable a wider investigation of the particularities of spontaneous arising of chromosome aberrations in somatic cells to be made at the present time.
The general questions which can be considered as referring to the theme of the report should be the following:
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the quantitative aspects of spontaneous chromosome aberrations, especially the influence of biological factors (age, sex) on frequencies ;
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the qualitative aspects, i.e. the types of spontaneous aberrations ; 3. the aberration frequencies in vivo and in vitro.
Quantitative Aspects
According to the data of different investigators the frequency of the chromosome aberrations varies widely: from 0 to 12.5~o aberrant cells (Chudina, 1968;Court Brown et al., 1966; Bochkov et al., 1968; Nielsen et al., t968). Partly, this can be explained by not sufficient experimental material, and partly, by differences in the estimate of the chromosome aberrations. The largest group was examined in Edinburgh. Over 12.000 cells were studied and it was revealed that 0.4% cells had chromosome aberrations (Court Brown et al., 1966).
This problem was studied in details in our laboratory where the information on 30.000 metaphases has been accumulated.