Figure 7.7 gives a pedigree for an autosomal recessive disease and a linked marker. The four marker genes

a, b,

c, and d are assumed distinct. If the recombination fraction between the two loci is θ, then show that the risk of the fetus 5 being affected is

(1 − θ)5θ + (1 − θ)4θ2 + (1 − θ)2θ4 + (1 − θ)θ5

(1 − θ)4 + 2(1 − θ)2θ2 + θ4