What evidence is given in the pedigree chart below to prove that the condition is caused by a dominant allele?

A. Two unaffected parents have unaffected children.
B. Two affected parents have affected children.
C. An affected parent and an unaffected parent have affected children.
D. Two affected parents have an unaffected child.

D

Most candidates answered this question incorrectly. Although it was a good question, it was perhaps a little bit too complicated for candidates to analyze a pedigree in such a short time. It was agreed at grade award that it would have made a better Paper 2 question.