How the multiple-factor hypothesis accounts for the 1:4:6:4:1 phenotypic ratio

How the multiple-factor hypothesis accounts for the 1:4:6:4:1 phenotypic ratio of grain color when all alleles designated by an uppercase letter are additive and contribute an equal amount of pigment to the phenotype.

P‘ AABB / aabb
i X
Red White
F. AaBb
Intermediate color
Additive alleles
r.
7 1/4 BB — 1/16 AABB #1 4
1/4 AA 77 1/2 Bb — 2/16 AABb fl 3
7 1/4 bb — 1/16 AM!!! 2
7 1/4 53 — 2/16 AaBB ‘ 4" 3
F2 1/2 A5 77 1/2 Bb — 4/16 A55!) 2
— 1/4 bb — 2/16 Aabb 1
7 114 BB — 1/16 aaBB 2
1/4 as 77 1/2 Eb — 2/16 alst 1
7 1/4 bb — 1/16 aabb o
l
Additive alleles
4 3 2 1 0
F2 ratio 1/16 ’ 4/16 6/16 4/16 1/16
1%
Red —> Intermediate colors —> White