A KARYOTYPE STUDY ON THE DROSOPHILA-ROBUSTA SPECIES-GROUP (DIPTERA, DROSOPHILIDAE)

The karyotypes of the Drosophila robusta species-group, especially its species-subgroup okadai, were studied by using brain cell-Giemsa stai ning method. Drosophila gani possessed a diploid number of 12 chromoso mes, comprising 4 pairs of metacentric and 2 pairs of acrocentric chro mosomes, and both D. okadai and D. neokadai did 2n = 12, with 3 pairs of metacentrics, 2 pairs of acrocentrics and 1 pair of microchromosome s. The okadai subgroup characteristically retained a middle-sized acro centric X chromosome, which implies that this subgroup may occupy an a ncestral position for the robusta group.