Interphase arrangement of rye B chromosomes in rye and wheat

Probes for B chromosome-specific sequences in the distal region of the long arm of the rye B have been used to investigate the interphase arrangement of the Bs in rye and in hexaploid wheat. The Lindstro¨m strain of wheat carries the rye Bs as additions. The number of in situ signals in nuclei with two, three and four Bs is often less than the maximum B number, and it seems that the Bs may be grouped together in various ways rather than being randomly dispersed throughout the nucleus. The degree of physical association is greater in rye than in the alien wheat background. The results are discussed in relation to the pairing and recombination preferences of the Bs in rye and in Lindstro¨m wheat.