Complementary Genes - In this type of gene interaction, the production of one phenotype requires the presence of dominant alleles of both the genes controlling the character. When anyone of the two or both the genes are present in the homozygous recessive state, the contrasting phenotype is produced.

Thus anyone of the two dominant genes is unable to produce the phenotype when it is alone. But the dominant alleles of the two genes complement each other to produce the concerned phenotype when they are together. This type of interaction shows a ratio of 9: 7.