The sexual size dimorphism of the control wing muscle hg1 is abolished in dsx^unspecified null mutant. In contrast to wild-type, he size of the hg1 muscle in dsx^unspecified mutant males is reduced relative to its size in females.

XY dsx^unspecified flies have intersexual external morphology.

Chromosomal females (XX) mutant for dsx are transformed into "pseudomales". They are sterile even in the presence of a Y chromosome. The gonads form testes which are generally non-gametogenic, containing degenerated germ cells and debris or gonial cells whose sex cannot be determined. A variable proportion are gametogenic, containing either oogenic or spermatogenic stages of germ cell development (never both in the same gonad). In these cases oogenesis is arrested anywhere between stages S3 and S10A, and spermatogenesis is frequently arrested at the spermatocyte stage, although some later stages of spermatogenic differentiation are seen.