- The Additional sex combs gene of Drosophila encodes a chromatin protein that binds to shared and unique Polycomb group sites on polytene chromosomes. Sinclair, D.A., Milne, T.A., Hodgson, J.W., Shellard, J., Salinas, C.A., Kyba, M., Randazzo, F., Brock, H.W. Development (1998)