Indirect DNA diagnosis in FAP

Linked DNAmarkers (RFLPs) near the APC locus
(1) can be used for indirect DNA diagnosis. The
alleles of three flanking marker pairs (K,k and
E,e on the centromere side and A,a on the distal
side) form the haplotypes, e.g., e–K–a and
E–k–a in individual I-1 in the pedigree (2). The
mutation-carrying haplotype must be e–K–a.
Since individual III-2 has inherited this haplotype,
he is at risk for the disease, whereas individual
III-1 is not.