Which of the following conditions represents a case of codominant genes

A gene expresses itself, suppressing the phenotypic effect of its alleles.

Genes that are similar in phenotypic effect when present separately, but when together interact to produce a different trait.

Alleles, both of which interact to produce a trait, which may or may not resemble either of the parental types.

Alleles, each of which produces an independent effect in a heterozygous condition.

Solution

Alleles, each of which produces an independent effect in a heterozygous condition.

Codominance is the phenomenon when the two alleles of a gene neither show dominant recessive relationship nor show intermediate condition, but both of them express themselves independently in heterozygous condition. This has been reported in roan coat colour of cattle (i.e., patches of two different colours on the skin).