Chromatid Separation Initiating from the NOR-bearing End of the Metaphase Chromosomes of Two Species of Aphis (Homoptera: Aphididae).

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Abstract
The localization of NORs in the somatic chromosomes of Aphis spiraecola Patch and A. craccivora Koch collected from the hosplants Solanum melongena and Dolichos lablab, respectively, was studied by the silver-staining method. In the interphase nuclei, frequently one or two, and rarely three silver-positive nucleoli appeared and continued to appear upto the early prophase. At metaphase, most of the plates revealed clearly the localization of NORs as tiny, round and deeply-stained dots at one terminal end of one pair of long chromosomes (pair no. 2) in the diploid complements (2n=8) of both the species. However, in a few slightly advanced metaphase plates in both the species, split NORs appearing as bifid structures were observed. The initiation of chromatid separation seemed to occur first from the NOR-bearing end in both the aphid species claimed to have holokinetic chromosomes.

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