An interpretation of the origin of subchromatid aberrations and chromosome stickiness as a category of chromatid aberrations.

Abstract

From a study of the effect of X irradiation on meiosis of the grasshopper Stethophyma grossum spermatocytes, it was deduced that the so-called “subchromatid aberrations” and the other effects which are generally referred to as physiological effects (i.e., stickiness, clumping and erosion of chromosomes) are in reality chromatid aberrations. The appearance of these aberrations results from the induction of breaks and exchanges in chromosomes during the prophase contraction, in which the chromatin fibers are held together in a three-dimensional organisation and cannot unfold. The origin of these kinds of aberrations can be explained on the basis of the folded fiber model of the chromosome. During meiosis in many organisms, a diffuse stage resembling the interphase nucleus (between pachytene and diplotene) is known to exist. If the diffuse stage is irradiated 48 hours or more before fixation with 500 R of X-rays, the diplotene folding is only partially realized and meiosis is blocked after the formation of an irregular network of chromatin fibers. The results indicate that although the diffuse stage looks like a regression to an interphase stage, the chromosome organisation is likely to be different. Irradiation with the same dose at a later stage (26 hours or less before fixation) does not prevent the course of meiosis.