Abstract
At first ana-telophase and second ana-telophase in the PMC's of Trillium kamtschaticum Pall. which were irradiated with X-rays at various stages from diplotene (presumed) to first metaphase, the diagnostic configurations of half-chromatid recombination, viz., 2-side-arm bridges were frequently observed. So far as the PMC's irradiated at stages from mid-prophase to first metaphase are concerned, the earlier is the meiotic stage of the cells, the lower is the frequency of 2-side-arm bridges resulted.
Almost all of 2-side-arm bridges are supposed to be brought about from exchange or union between two non-sister half-chromatids of two associated chromatids, whose possibility is suggested from spatial relationship of the four chromatid threads in a bivalent at late prophase and first metaphase.
The present findings indicating that the occurrence of 2-side-arm bridges is so frequent regardless of the number and position of interstitial chiasmata may well be explained on the basis of Matsuura's Neo-two plane theory, that is, free two-by-two disjunction of the four sister kinetochores of a bivalent at anaphase after free opening-out of the chromatids at diplotene.
