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.
The general outline of meiosis proposed by Wilson in 1925 included a diffuse stage following pachytene or early diplotene, although such a stage may be missing in some organisms. Different forms of such a stage are known to exist in male and female meiosis of many animals, but usually they are treated separately and not included as a special stage in the scheme of meiosis in modern textbooks.
It was shown by a literature research that, up to 1940, the existence of a diffuse stage was recorded in meiosis of many plants (the sectioning technique used at this time made it easy to follow accurately the sequence of meiotic stages) but few authors considered this stage to be a common part of plant meiosis. Its existence was actually observed by many authors at this time, but it became a common tendency to regard it as due to “bad fixation”, or “fixation artefacts” only. Remarks about the existence of such a stage disappeared after the introduction of squash techniques, but started to reappear after 1960. Today, references about the existence of a diffuse stage are known from all groups of plants (Angiospermae, Gymnospermae, Pteridophyta, Bryophyta, Fungi, Algae). The conception of meiosis published by Wilson is thus found to be more close to reality and therefore it is proposed that such a concept is accepted as a general outline of meiosis.
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