Abstract

The presence of rRNA genes on homoeologous chromosomes 1A, 1B, and 1D of hexaploid wheat was investigated by rRNA/DNA hybridization, using DNA purified from aneuploid and substitution line derivatives of the variety Chinese Spring. Doubling the number of 1B chromosomes increased the number of rRNA genes by 31–49% but deleting the 1B chromosomes decreased the number by only 15–23%. This suggests that changes may occur in rRNA gene multiplicity at other nucleolar organizer sites to partially compensate for a deficiency of rRNA genes. There was no unequivocal evidence of rRNA genes on Chinese Spring chromosome 1A or 1D, but other varieties were shown to have rRNA genes on chromosome 1A. These results are consistent with the cytological observations that chromosomes 1A and 1B but not 1D possess nucleolar organizers.

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