The genetics of an ethyl methane-sulfonate-induced mutation, Deep throat (dt), was investigated. Experimental data indicate that Dt is recessive and sex-linked. The gene sequence is dt-go-w-M and the recombination frequencies are as follows: dt-go=15.02%; dt-wre=23.28%, and dt-M=37.65%. This mutant currently represents on terminal marker on linkage group I which is approximately 39 map units in length.