The soybean trypsin inhibitor (SBTI-A2) is a seed protein that exhibits different electrophoretic forms. Hymowitz and Hadley (1972) demonstrated that two different electrophoretic fonns of SBTI-A2 represent the expression of two codominant alleles at a single locus. They assigned the symbol Ti1 to the allele controlling the most commonly occurring electrophoretic form Rf 0.79/10% (Rf= mobility relative to the dye front in a 10% polyacrylamide gel anodic system) and Ti 2 to the allele controlling the electrophoretic form found at Rf 0.75/10%.