A Strain of a Cereal Grain Can Be Either Dark

Short Answer

A strain of a cereal grain can be either dark tan, medium-dark tan, medium tan, light tan, or
cream colored. When a dark tan and a cream plant are crossed, all F₁ are medium tan. The F₂ are distributed in a ratio of 1:4:6:4:1 from darkest to lightest. How many additive alleles are needed
to produce the darkest phenotypes?