COMPARATIVE DESCRIPTION OF THE EFFECTS ON THE CORN GRAIN OF THE OPAQUE•2 (O2) AND FLOUR •2 (fl2) GENES.

Abstract

The opaque -2 and floury- 2 genes modify the pro te in of the
endosperm of corn, acting as inhibitors of lhe synthesis of zein
(protein of low quality) that results in a larger relative proportion of
the essential amino acids lysine and tryptophan. However, these
genes vary in the magnitude oí their effects in protein and in other
physical characteristics of the grain. The inheritance of  o₂ is recessive and that of fl₂ semidominant and depends on the genetic dosage in the endosperm far the quality of the protein. In o₂ a triploid
homozygous condition is necessary to produce the high quality
protein. Opaque- 2 doubles both the lysine and tryptophan content, reduces total protein of the endosperm and increases the weight of the germ in the crosses and sib increases. Floury- 2 is less effective
in increasing lysine and tryptophan and more inconsistent, but
increases the conlent of methionine and protein of the endosperm in some backgrounds; the weight of whole grain is reduced more in o₂ genotypes than in floury-2. the size of grain es increased in floury-2 and is maintained donstant in o₂. the loss of density is similar for both mutants. Opaque-2 kernels retain more humidity and floury-2 kernels retain less than normal kernels. the types of protein and the respective proportions in the differents parts of the grain of o₂, fl₂ and normal maize kernels are described.