Cytogenetic analysis of the holocentric chromosomes of the aphid Schizaphis graminum

Chromatin organization in the holocentric chromosomes of the aphid Schizaph is graminum has been investigated at a cytological level after C-banding, N OR, Giemsa, DAPI and CMA(3) staining. C-banding technique showed the presen ce of numerous C bands on the two X chromosomes both in telomeric and inter calary regions, whereas autosomes show a small number of heterochromatic ba nds. Contrary to the results with other aphid species, in S. graminum the C -banding pattern is peculiar to each chromosome pair, thus allowing the ide ntification of homologues and the reliable reconstruction of a karyotype. T hese cytogenetic data could be useful for the identification of chromosomal rearrangement eventually occurred between different S. graminum biotypes. Moreover, silver staining and fluorescent in situ hybridization (FISH) with a 28S rDNA probe localized rDNA genes on one telomere of each X chromosome ; these are the only brightly fluorescent C-positive regions revealed after CMA(3) staining, whereas all other heterochromatic bands are DAPI positive .