The pedigree diagram below shows the inheritance of phenylketonuria (PKU), a genetic disorder caused by a single gene with two alleles.
Based on the diagram, what is the probability that child 8 will be affected by phenylketonuria?
0.250.250.25 (or 25%25\%25%)
0.330.330.33 (or 33.3%33.3\%33.3%)
0.500.500.50 (or 50%50\%50%)
0.670.670.67 (or 66.7%66.7\%66.7%)
