a1 Institute of Genetics, Biological Research Centre, Hungarian Academy of Sciences, H-6701 Szeged, P.O. Box 521, Hungary
a2 Department of Biology, Williams College, Williamstown, MA 01267, U.S.A.
A second chromosome line of Drosophila melanogaster (S-90), isolated from a northern California natural population, is able to induce (1) an increased frequency of X-chromosome visible mutations, (2) male recombination activity subject to reciprocal cross suppression, and (3) strong meiotic drive from heterozygous males. Based upon several lines of evidence (including the response to suppressor chromosomes of both systems) we conclude that S-90 contains both SD (Segregation Distortion) and MR (P or I) chromosome activity. The two systems appear to behave independently and simultaneously, and a small centromeric region of the S-90 chromosome appears to contain the major genetic elements of both systems.
(Received March 16 1983)
(Revised June 30 1983)
p1 Present address: Plant Protection Institute, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 102, Hungary.