Use of gene substitution values to quantify partial dominance in low palmitic acid soybean

Several low palmitic acid mutants have been developed in soybean [Glycine max (L.) Merr.] to improve oil. quality. Single locus mutations have been identified which control low palmitic acid: fap1 allele in C1726 and fap3 allele in A22. Each allele was found to be additively inherited at the intralocus level. There is less understanding of the inheritance of low palmitic acid controlled by alleles at more than one locus. The objectives of this study were to: (i) determine the number of loci and type of gene action associated with the cross between two low palmitic lines, and (ii) propose a simple calculation method that accounts for partial dominance at the intralocus level. Two independently developed low palmitic lines (ELLP2 and C1726) were crossed. The analyses of F-2 and F-3 generations indicated that the combination of alleles at two loci (temporarily designated Fap* locus in ELLP2 and the previously described Fap1 locus in C1726) were controlling the transgressive segregation of palmitic acid. The Fap* allele was partially dominant over the mutant fap* allele in ELLP2. A simple calculation method was proposed to account for the degree of dominance in order to explain and predict the F-2 segregation in the ELLP2 x C1726 cross. The (ELLP2 x C1726) F-2 seeds segregated into six distinct phenotypic groups that fit a 1:2:3:5:4:1 ratio. The ratio corresponded well with the expected genetic pattern on the basis of the gene substitution values. The results indicated the segregation of two loci in the ELLP2 x C1726 cross: Fap* with partial dominance and Fap1 with additive gene action, and no epistasis at the interlocus level. Furthermore, the calculation based on gene substitution values may be used in predicting other complex segregation ratios.