Past exam of the mathematics course of the University of Cambridge / 2001 / iii / Paper 29 / 6 / ii

The individuals' haplotypes are not identifiable from the supplied source: the pedigree drawings are missing. The original PDF has a blank figure area, and the accompanying TeX contains no family genotypes. Even the two-locus genotypes of individuals 3 and 4 are not stated elsewhere, so numerical allele pairs cannot be supplied honestly.

The method, once the drawings are available, is to use parental or grandparental genotypes to assign the allele inherited at each locus on the same chromosome. A double heterozygote with alleles $A_1,A_2$ and $B_1,B_2$ has the two candidate haplotype pairs $A_1{B}_1/A_2{B}_2$ and $A_1{B}_2/A_2{B}_1$; ancestor and offspring transmissions determine or restrict its phase. These symbols describe the general phasing problem, not invented genotypes for the missing individuals. If pedigree transmissions leave more than one phase possible, retain all compatible phases rather than selecting one without evidence.