A  female  calico  cat  shows  random distribution of orange and black
   patches  of  fur.  The  gene  for  this  locus  is X-linked. Since the
   inactivation  of  X  chromosomes  occurs  randomly  early in embryonic
   development,  all progeny cells from the embryonic precursor cell have
   the  same X chromosome inactivated, causing a patchy expression of the
   alleles.

   The white patches are due to a separate epistatic "spotting gene" that
   prevents pigments from migrating to the skin.