Figure 1.

Progeny from crosses to C(2)EN. As C(2)EN males contribute gametes that carry the gene dosage of either two or zero copies of chromosome 2, only progeny that also inherit zero or two copies from the other parent will result in viable euploid progeny. Note that sex determination in Drosophila uses the ratio of X to autosomal chromosomes, and that the Y chromosome is not masculinizing as in mammals (Ashburner et al. 2005). This means that flies with one dose of X chromosome genes develop as males and flies with two doses of X chromosome genes (either free or attached) develop as females, while having three doses (including C(1)EN/X) is lethal.