Chromosomal localization of a highly repeatedEcoRI DNA fragment inMegoura viciae (Homoptera,Aphididae) by nick translation and fluorescencein situ hybridization

To investigate the genome of the aphidMegoura viciae at molecular level, we have studied total DNA by agarose gel electrophoresis after cleavage with different restriction endonucleases.EcoRI digestion produced a highly repeated DNA fragment, about 600 bp long. The contribution of thisEcoRI element to the total genome ofM. viciae was estimated at about 6% by means of densitometric scanning of agarose gel photographs. The chromosomal localization of this fragment, investigated by fluorescentin situ hybridization (FISH), constantly showed one large and two narrower fluorescent bands located on the X chromosome, all corresponding to C-positive heterochromatic areas. These results are in full accordance with the data obtained byin situ nick translation experiments carried out afterEcoRI digestion, and clearly demonstrate that a substantial amount ofM. viciae heterochromatin consists ofEcoRI fragments which are mainly located on the X chromosome. Using theEcoRI restriction fragment as a molecular probe may prove to be a practical tool for the investigation of taxonomic and evolutionary relationships in this group of insects.accepted for publication by J. S. (Pat) Heslop-Harrison