In  Drosophila,  the wild-type
   red eye color is dominant to white eyes.

   Reciprocal  crosses  between  white-eyed  and  red-eyed  flies  yields
   different results.

   The results indicate the white (w) locus is X-linked (present on the X
   chromosome).

   Males  carry  only  one  allele  for  X-linked  genes  and  are called
   hemizygous.