In epistasis an allele of one gene suppressed or masked the phenotypic expression of a gene at another locus. The gene which masked is called hypostatic gene, In complementary gene interaction, the production of one phenotype requires the presence of dominant alleles of both the genes controlling the character. In duplicate gene interaction, the presence of a single dominant allele of any one of the two genes governing the trait produces the dominant phenotype. The recessive phenotype is produced only when both the genes are in homozygous recessive state. In supplementary gene interaction the dominant allele of one gene is necessary for the development of concerned phenotype while that of the other gene modifies the phenotypic expression of the first gene.