Allele-specific    oligonucleotides
   (ASOs)  synthesized  from  normal and mutant alleles and cloned by PCR
   can screen for the D508 deletion in cystic fibrosis (CF).

   DNA from the parents (I-1 and I-2) hybridizes to both ASOs, indicating
   that they are heterozygous.

   DNA  from II-1 hybridizes only to the D508 ASO, indicating that she is
   homozygous for the mutation and has CF.