The diagram shows a pedigree.

According to the pedigree shown, which pattern of inheritance is indicated?

A. Sex-linked recessive trait
B. Autosomal recessive trait
C. Autosomal dominant trait
D. Codominant alleles

C

Three teachers expressed concern over this question suggesting that it is not possible to rule out codominance. Codominance would be indicated as a third colour in the pedigree and all offspring of the first generation parents would need to be represented by the intermediate phenotype.