The influence of B-chromosomes of Secale cereule on chromosome association at metaphase of the first division of meiosis on an inter-varietal T. aestivum hybrid Chinese Spring x Lindstrom (carrying rye Bchromosomes) was studied in the presence and absence of chromosome 5D of wheat.
The presence of rye B-chromosomes did not change the normal pattern of chromosome association in disomic and significantly though slightly increased chiasma frequency in monosomic 5D plants at 2O'C. When chromosome SD was absent, this increase was more pronounced, especially in respect to the number of ring bivalents. It is suggested that this increase is a consequence of an additive effect of post-synaptic gene(s) in rye B-chromosomes which locally increased chiasma frequency in A-chromosomes, and of the absence of (a) desynaptic gene(s) of chromosome 5D. Even in nullisomic 5D plants, at 10ยฐC, where a high degree of asynapsis was observed, the addition of B-chromosomes increased chromosome association, but then there was no observable increase in the monosomics, which at 10ยฐC did only show a slight reduction in pairing. introduction The chromosomes of the three constituent genomes of hexaploid wheat, Triticum aestivum (2n = 6x = 42) * The work was supported by a fellowship of the Gulbenkian Foundation and partly carried out while the author was at the