In situ hybridization confirms jumping nucleolus organizing regions in Allium

In situ hybridization with a ¹²⁵I-rDNA clone from Vicia faba was performed against Allium cepa and three strains of top onion, which represent hybrids between A. cepa and A. fistulosum. In principle, the labelling patterns correspond to the patterns of the silver-stained nucleolus organizing regions (NORs) in the same species. This strongly supports the inference drawn from the Ag-NOR patterns that NORs can jump between terminal heterochromatin blocks of different Allium chromosomes in the parental species A. cepa as well as in their interspecific hybrids.