A three-point mapping cross involving the yellow (y) body color, white
   (w) eye color, and echinus (ec) eye shape genes in Drosophila.

   In  the F[1], females are heterozygous at all three loci and males are
   hemizygous for the mutant alleles.

   Most  of  the F[2] show parental (NCO) phenotypes, with DCOs the least
   common among the recombinants.