Karyotype differentiation among members of the immigrans species group of Drosophila.

Karyotypes of ten species belonging to four of the five subgroups of the immigrans species group of Drosophila were examined. The group includes species with the most primitive form of karyotype as well as species with so-called recent karyotypic configurations. It is an assemblage of species with karyotypes representing five of the six successive stages involved in the evolution from 2n = 12 to 2n = 6. Implications of these findings are discussed.