Affected Members of the Pedigree Above Have an Autosomal Dominant

Essay

Affected members of the pedigree above have an autosomal dominant disorder, and cytogenetic analyses using conventional chromosome banding did not identify a disease-associated chromosomal abnormality. However, recent previous studies in other families mapped the disease locus to a region on the short arm of chromosome 17 and showed that four polymorphic microsatellite markers, P, Q, R and S are closely linked to the unidentified disease locus. (The order of the markers from most distal to most proximal is given by the following sequence: P-Q-R-S). When the same four markers were used to genotype each member of the family above, the alleles obtained were as listed below.

a) If we were to assume that the disease locus is also at the same 17p region in this family, what is the disease haplotype originating from I-2 (that is, the sequence of alleles at the four marker loci on the chromosome that has the disease allele)?
b) Has the disease haplotype been conserved in all family members?
c) Is it likely that the disease in this family is linked to 17p?
d) If the disease locus were to be at 17 p in this family, what do you deduce about the position of the disease locus with respect to the marker loci?