A woman trying to get pregnant has a sister whose child has an autosomal recessive disease characterized by dysfunction of mucus-secreting cells. As a result, this child has abnormally thick mucus that tends to precipitate into dense plugs that obstruct the pancreatic ducts, bronchi, and bronchioles, as well as the bile ducts. Which of the following tests could be performed to determine if this woman and her husband are carriers of this disease?

The disease described is cystic fibrosis, which phenotypically presents with meconium ileus, deficiencies of pancreatic enzymes, pulmonary obstruction and infection leading to progressive pulmonary damage and ultimate respiratory failure. The most frequent mutation in this autosomal recessive disorder is a small deletion of a phenylalanine at position 508. An amplification of this region using PCR can be done and then that poion sequenced to see how it compares to the normal sequence. Nohern blot is used to determine RNA levels inside a cell and would not help us determine if this person is a carrier. Southern blots are used to study genomic DNA on a gross level and could not be used to see a single base-pair deletion. Western blots are used to look for the presence or absence of a paicular protein, but since the protein is produced, though defective, this technique would not give the information needed.