[Variation in the number of C-heterochromatin blocks in the interphase nuclei of the cells of a transplantable murine rhabdomyosarcoma].

By means of staining procedure which reveals the constitutive heterochromatin (CH), the number of CH-blocks was detected in the nuclei of interphase cells obtained from the subcutaneously growing rhabdomyosarcoma and from its 10 lung colonies. The range of variability of the number of CH-blocks in tumor cell populations was greater than in the populations of normal lung cells and lymphocytes. The mean numbers of CH-blocks varied from 17.8 +/- 0.9 to 28.0 +/- 1.2 in cells of different clones, the mean number of CH-blocks in clones being the same as in the subcutaneously growing uncloned tumor. The coefficient of heritability h2 of character "the number of CH-blocks", calculated on the basis of population and interclonal variances, was equal to 0.15, and that calculated by one-factor dispersional analysis was actually the same (0.16). It is concluded that the high heterogeneity of tumor cells may be conditioned not only by their high phenotypic instability, but also by a high frequency of mutations.