Abstract
Variation in restriction pattern, relative amounts of the two ribosomal DNA (rDNA) repeats, and the overall content of rDNA were compared among twelve segmental duplications and eleven parental translocations involving NOR6 and NOR7 of cultivated barley. Southern blot hybridization revealed two rDNA repeats of 9.9 kb and 9.0 kb. While all duplications showed dimers for these rDNA repeats, the duplication lines D29 and D47 displayed trimers in addition to a higher proportion of rDNA repeats as dimers. The rDNA of Dl, D29 and D47 showed re nce to Bam HI and Tdq I digestion, indicating possible methylation of cytosine and adenine. Densitometric scans of autoradiographs revealed variations in the relative amounts of the 9.0 kb and 9.9 kb rDNA repeats among different karyotypes. Dot blot hybridizations indicated variation in the overall rDNA content. Comparison of the 9.0i9.9 kb ratios and the percentage of' genomic DNA hybridizing to an rDNA clone of barley illustrates differential amplification for thc two rDNA repeats. When the segmental composition of lhese deviating lines were compared, it was evident that the relative position of the segment 12-16 of chromosome 6 determines differential amplification whilc duplication of the same segment controls the overall rDNA content.
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