5. My working hypothesis on the yellow-orange endosperm is now as follows:
(a) Several Y-genes with complementary effects, similar to the A1A2A3C R series for aleurone color. Of the Y-series, the known genes are Y1 in chromosome 6, Y3 in chromosome 2 and probably Yx of Dr. Brunson, chromosome unknown. The yx condition is lethal and the y3 produces albescent seedlings (al gene).
(b) The Y5 gene, isolated from Brazilian strains is complementary to Y1 in producing yellow endosperm but is independent of Y3 and so, also, of the other Y-genes of the series.
(c) The YD gene (D=determiner) producing the difference orange : yellow, found in Brazilian material and extremely influenced by modifiers. Similar gene found recently by Dr. Jenkins in chromosome 7.
(d) The Bn gene in chromosome 7, producing yellow pigment only in the aleurone layer. These "lemon yellow" seeds are detectable in stocks lacking one of the complementary Y-genes for endosperm color.