This version was published by NRC Canada http://pubs.nrc-cnrc.gc.caThe nucleolar activity in interspecific hybrids between tritordeum, wheat, and triticale was studied using the silver salt – nylon technique. rRNA genes from the major NORs from wheat (chromosome pairs 1B and 6B) and Hordeum chilense (chromosome pairs 5Hch and 6Hch) were active in genomic constitutions AABBHchHch, AABBHch,\ud and AABBDHch. The rye chromosome 1R NOR suppression found in triticale and in wheat × rye F1 hybrids is also observed in trigeneric hybrids, genome constitution AABBRHch, derived from crosses between triticale and tritordeum. As expected, the maximum number of NORs per metaphase cell is coincident with the maximum number of nucleoli per interphase cell. Occasional extra nucleolar activity was observed, probably owing to minor sites of wheat NORs,\ud since no other sites of active or inactive rRNA genes were detected in H. chilense. However, it is notable that the two\ud H. chilense loci and two major rDNA loci of wheat origin are expressed together
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