Abstract
Presumptive clones of human skin fibroblast-like cells surviving mitomycin C treatments show a variety of intra- and interchromosomal rearrangements limited to the constitutive heterochromatic regions. Starting with a wild-type line polymorphic for chromosome no. 1 heterochromatin, we have observed clones with complete symmetry and varying degrees of asymmetry of the no. 1 heterochromatin, translocations of “excess” chromosome 1 heterochromatin to one no. 9 member, interstitial translocations to sites normally devoid of heterochromatin, and duplication of the Y chromosome long arm heterochromatin. In the case of the chromosome no. 1 pair, the extent of heterochromatin variation was quantitated to test the hypothesis that discrete classes of variants occur. There appear to be two types of variants: Those showing reciprocal changes between homologues (2 examples) and those showing a change in the amount of heterochromatin of a single homologue (5 examples). The latter group showed an approximately linear series of variants. Unequal cross-over following repair after damage from the alkylating agent is considered the most likely explanation for the observed changes, given the repetitive nature of DNA at these heterochromatic sites.
Published Version
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