Figure 1.

Dicentric chromosome formation mediated by FLP recombinase with the DcY(H1) chromosome. The DcY(H1) chromosome is a B^S Y y⁺ chromosome carrying inverted FRTs inserted proximal to B^S on YL, but distal to all fertility factors. FLP-mediated recombination between inverted FRTs on sister chromatids produces a dicentric Y chromosome, and a small acentric chromosome carrying both copies of B^S. In mitosis, the dicentric bridge breaks to produce daughter cells, each carrying a chromosome with one broken end. If these chromosomes are healed and transmitted to progeny they may be recognized as y⁺ B⁺ offspring. Dicentric chromosome formation on other chromosomes uses inverted FRTs to similar effect.