Chromosome Studies an Trillium kamtschaticum Pall XII

The mechanism of crossing-over

Abstract

1) The paired chromatids of each meiotic chromosome constitute at early metaphase the relational spiral system (Fig. 1A), while those at late metaphase take the parallel system (Fig. 1B).
2) This conversion of the spiral system takes place first from the proximal region and then independently from the distal end. These processes proceed inwards along the arm and when they meet one another the parallelisation is completed.
3) Such an orientation of the parallelisation excludes a possibility that the system is altered by rotation of the free end. The other possibility must, therefore, be admitted that the parallelisation is associated with breaks and reunions between the chromatids at twisting points existing in the spiral system. This breakage is supposed to be caused by the cleavage of the matrix enveloping the minor spiral, which at the same time plays a rôle for preventing the transversal reunions of the broken ends (Fig. 26).
4) According to the writer's Neo-two-plane theory, the paired chromatids are non-sisters in two-thirds of the Gases. Therefore in these cases such breaks and reunions should result in detectable crossovers.
5) This new hypothesis of crossing-over mechanism presents reasonable expianations for many essential characteristics hitherto known in the crossing-over phenomena.