Question

In the F₂ generation of the three-gene skin colour cross (AaBbCc × AaBbCc), what phenotype corresponds to 6 contributing alleles?

Options

• Very light skin colour

• Lightest skin colour

• Darkest skin colour

• Intermediate skin colour

Answer 1

When an individual has 6 contributing alleles (AABBCC genotype), they possess the maximum number of dominant alleles possible in a three-gene model, resulting in the darkest skin colour phenotype. As the number of contributing alleles decreases, the skin colour progressively lightens, demonstrating the additive nature of polygenic inheritance where more contributing alleles produce a more extreme phenotype.