Familial Down syndrome.

   One parent contains a 14/21 translocation and has only 45 chromosomes,
   and is a phenotypically normal carrier.

   1/4  of  the  individual's  gametes  will  have  almost  2  copies  of
   chromosome 21.

   The  resulting  zygote  has  46  chromosomes,  but  almost 3 copies of
   chromosome 21, and exhibits Down syndrome.