Eight different strains of Drosophila have been isolated; each shows a recessive white eye trait. Crosses were performed as follows (W indicates white-eyed progeny, R indicates wild-type red eyed progeny).

A B C D E F G HA W W R R W R R WB W R R W R R WC W W R R R RD W R R R RE W R R WF W W R
G W RH Wa) Based on these crosses, how many different genes are present?