Chromosome behaviour and structural hybridity in the tradescantiae. II.

Abstract

1. Fragments pair with major chromosomes inTradescantia by lateral chiasmata whose chromatid structure is revealed by pre-treatment. They do not then develop the usual major spiral. 2. Less contracted chromosomes in mutant cells have more coils. Spiralization therefore consists in reducing the number of coils. 3. Interlocked chromosomes, like multivalents, may have linear, twisted, or discordant orientations according to the method of interlocking. 4. The type of distribution of the bivalents on the metaphase plate inT. bracteata depends on the numbers of their chiasmata and on the radial or tangential adjustment of the individual bivalents. 5. The central chromosomes of the metaphase plate are pushed to the edge of the group during anaphase in some forms and species. This change may take place asymmetrically both at mitosis and meiosis. It shows that the repulsion from the poles is still acting on the chromosomes while they are moving towards the poles. Thus the anaphase in some forms comes to correspond with the hollow metaphase in others. 6.Rhoeo discolor and diploid, triploid and tetraploid species ofTradescantia show the results of inversion crossing-over under normal conditions. Fragments are small inRhoeo and in the tetraploids, showing that the assumption of pairing and crossing-over being restricted to the end regions is justified.