Allele-specific oligonucleotides (ASOs) synthesized from normal and mutant alleles and cloned by PCR can screen for the Δ508 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 Δ508 ASO, indicating that she is homozygous for the mutation and has CF.