The structure of the holocentric chromosomes of the rosy apple aphid, Dysaphis plantaginea (2n = 12), and pear-grass aphid, Melanaphis pyraria (2n = 8), was studied using C-banding, NOR, Giemsa and fluorochrome staining, and fluorescent in situ hybridization (FISH). Contrary to the equilocal distribution of heterochromatin typical of monocentric chromosomes, in both species C-banding evidenced a tendency of highly repetitive DNAs to be restricted to the X chromosomes. Silver staining and FISH, using a 28S rDNA probe, located rDNA genes on one telomere of each X chromosome, the only brightly fluorescent C-positive sites revealed by CMA3 staining, whereas all other heterochromatic C-bands were DAPI positive. Both species showed a noticeable amount of rDNA heteromorphism. Mitotic recombination is proposed as a possible mechanism responsible for the variation in size of rDNA.
Criniti, A., Simonazzi, G., Cassanelli, S., Ferrari, M., Bizzaro, D., & Manicardi, G. C. (2009). Distribution of heterochromatin and rDNA on the holocentric chromosomes of the aphids Dysaphis plantaginea and Melanaphis pyraria (Hemiptera: Aphididae). European Journal of Entomology, 106(2), 153–157. https://doi.org/10.14411/eje.2009.018