Final answer:
The Duplicate Gene Action epistasis ratio typically results from a genetic interaction where either of two genes can mask the expression of the other. For example, in the shepherd's purse plant, a cross between heterozygotes at both loci yields a phenotypic ratio of 15 triangular seeds to 1 ovoid seed, due to dominant epistasis.
Step-by-step explanation:
The Duplicate Gene Action epistasis ratio refers to a type of genetic interaction in which two genes duplicate each other's action, such that either gene can mask the expression of the other. In cases where the phenotype depends on two different genes in a dominant epistasis relationship and a cross is made between individuals heterozygous for both genes, the phenotypic ratio observed in the offspring may differ from the classic Mendelian dihybrid cross of 9:3:3:1.
For instance, in the shepherd's purse plant (Capsella bursa-pastoris), when both genes A and B are homozygous recessive (aabb), the seeds are ovoid. If either gene contains a dominant allele, the seeds are triangular. Therefore, a cross between individuals heterozygous at both loci (AaBb x AaBb) will lead to a phenotypic ratio of 15 triangular seeds to 1 ovoid seed. This 15:1 ratio is indicative of a dominant epistatic interaction, where the presence of at least one dominant allele in any of the two genes will determine the trait expression.