Tutto creste incroci dominanze ecc.

Digenic epistatic relationships as which the interaction between two genes was found to produce a "new" phenotype.

Wyandotte "rose-comb" have the genotype RRpp, while Brahma "pea-comb" have the genotype rrPP. A cross between a Wyandotte and a Brahma would yield offspring that all had the RrPp genotype, which manifested as a new type of comb "walnut-comb" phenotype (neither the rose comb of the Wyandotte nor the pea comb of the Brahma appeared to be dominant). A chicken with at least one rose-comb allele (R) and one pea-comb allele (P) would have a "walnut-comb". When two F1 "walnut-comb" chickens were crossed, the resulting F2 generation would yield in a 9:3:3:1 ratio : 9 "walnut-combs" (R_P_), 3 "rose-combs" (R_pp), 3 "pea-combs" (rrP_), as well as 1 "single-comb". These "single-comb" chickens have the rrpp genotype.

So we could say "single-comb" is recessive to "pea-comb" & "rose-comb" but these are not dominant to single comb ... but epistatic to it. (Similar to recessive white gene (c/c) suppressing all color in plumage, regardless of all color/pattern genes present).