Human chromosome 9 pericentric homologies: implications for chromosome 9 heteromorphisms

Pericentromeric polymorphisms of chromosome 9 include variations in the siz e of heterochromatin, pericentric inversions, and, more rarely, additional C-band-negative, G-band-positive material in either the proximal short arm or long ann or within the heterochromatin. It has been postulated that rear rangements involving the different classes of satellite DNA present in this relatively unstable region of the human genome constitute a mechanism for the origin of these variants. We report the identification, by molecular cy togenetic investigations, of homologous stretches of euchromatin shared by the proximal short and long arms of chromosome 9 that suggest that exchange s involving these regions may be an additional mechanism for the origin of chromosome 9 polymorphisms.