Shell  coiling  in  the  hermaphroditic  snail  Limnaea peregra may be
   right-handed (dextral) or left-handed (sinistral).
   The coiling depends on the genotype of egg donor parent, regardless of
   the phenotype of that parent.

<LI> If that parent is DD or Dd, the offspring will be dextral.
<li> The   dominant  allele  (D)  produces  a  gene  product  that
influences spindle orientation in the first cleavage division
of   the  zygote,  which  in  turn  affects  subsequent  cell
divisions to produce permanent coiling in that direction.