Autosomal  Recessive  Trait.  Since neither II-3 nor II-4 is affected,
   this must be a recessive trait that has skipped a generation; and II-3
   and  II-4  must  both  be  heterozygous.  Approximately  1/4  of their
   offspring  should  be  affected,  and II-3 and II-4 individuals can be
   represented by a shaded dot within their symbols.