Since all F[1] offspring had red
   eyes,  the  mutant  white-eye  trait  (w)  must  be  recessive  to the
   wild-type red-eye trait (w^+).
   Since the recessive white-eye trait was expressed only in males in the
   F[2]  generation,  the  eye-color  gene  must  be  located  on  the  X
   chromosome: sex-linked.