Skin pigmentation is determined by two genes and a woman is heterozygous for one gene and homozygous for other gene. She exhibits the homozygous trait herself and this is an example of

The correct option is A Epistasis
Epistasis is the nonallelic gene interaction where the presence of one gene masks or alters the expression of another gene thereby not allowing the later one to express fully. In the given example, the gene present in the homozygous state has masked the effect of another gene, hence it is epistasis. Pleiotropy is the condition where a gene has its own independent effect but also modifies the expression of a completely different gene quantitatively. Here, one gene is masking the expression of another gene of the same trait. X linkage refers to inheritance of trait with that of X chromosome. Codominance and dominance are the allelic interaction of the same gene.

Therefore, the correct answer is option A.