Polyacrylamide gel electrophoresis of PCR products from members of family 2 digested with the restriction endonuclease Sac II. The undigested PCR product (lane 1) gives a single 253-bp band. DNA from a nonaffected member is completely digested (lane 2), showing two bands of 137-bp and 116-bp, respectively. DNAs from the three affected members of the family (lanes 3 to 5) show digestion of the normal allele (the 137-bp and the 116-bp bands), whereas the mutated allele is not digested and appears as the original 253-bp band.