Figure 4.

The X:A ratio determines sex in Drosophila melanogaster. In Drosophila melanogaster sex is determined by the X:A ratio, which is communicated through the balance between the X numerator elements and the autosomal denominators in the presence of several maternally derived proteins. An X:A ratio of 0.5 leads to a non-functional SXL and male development, whereas an X:A ratio of 1 maintains SXL in its active state and is conducive to female development.