Two pure-breeding wheat strains, one producing dark red kernels and the other producing white kernels, are crossed to produce F₁ with pink kernel color. When an F₁ plant is self-fertilized and its seed collected and planted, the resulting F₂ consist of 160 plants with kernel colors as shown in the following table. Kernel Color Number White   9 Dark red 12 Red 39 Light pink 41 Pink 59 How many additive alleles are required to explain the five phenotypes seen in the F₂?