Correct Option: A

Epistasis refers to the phenomenon in which one gene hides the effect of the other. In other word, it does not allow the other gene to express itself. This is counterpart of dominance. While dominance works at inter allelic but intragenic level, Epistasis works at inter generic level. Epistasis is of following types: ·
Due to a recessive allele: A hides the effect of B, ·
Due to a dominant allele: A hides the effect of B.
This may be in one direction only meaning that either A hides the effect of B or vice versa.