Published online by Cambridge University Press: 14 April 2009
A genetic analysis was made of the Female-lethal (Fl) locus of Drosophila melanogaster. This is an X-linked mutation which causes lethality only in females. Other alleles do not complement Fl and are either lethal or sterile when homozygous in females. Complementation studies on Fl alleles demonstrate that there is no simple ranking of these alleles in terms of severity of phenotypic effect. Dosage manipulation of Fl alleles indicates that the sex-specificity is not a consequence of gene dosage effects. Viability studies on males carrying Fl alleles show that Fl alleles have no effect on viability regardless of the presence or absence of a Y chromosome. The Fl locus is therefore sex-specific. The hypothesis that Fl+ is involved in the establishment of imaginal phenotypic sex cannot be substantiated on the basis of experiments utilizing sex-change mutations.