Question

Epistasis and complementary genes are different. Justify the statement with a reason.

Answer 1

Hint: Genes are small DNA fragments that have a particular nucleotide sequence which encode a particular gene product like protein or RNA. Genes usually express themselves individually but at times the genes present on different alleles have influence on each other. This is known as gene interaction.

Complete answer:
Complementary genes are those genes which are present on different locus but these interact to give dominant phenotype. If they are present alone they will not be able to express themselves. Hence, they are said to complement each other. The presence of both of them is necessary for their expression.

A gene which masks or hides the expression of another non-allelic gene is said to be an epistatic gene and the phenomena is known as epistasis, while the gene whose effect is masked is known as the hypostatic gene.

Now the epistasis is of two types:
> Recessive Epistasis - Here the expression of the dominant gene is masked by the recessive allele in the homozygous condition.

> Dominant Epistasis - Here the expression of recessive genes is masked by the dominant allele of the other gene.
Therefore, epistasis and complementary genes are two different things.

Note: Epistasis occurs when one gene is able to mask the phenotype of another gene. Here it must be noted that the expression of the purple colour in a pea flower is due to two genes, gene C and gene P. In the absence of either of these two genes white flowers are produced. Hence, these two genes, gene P and gene C are complementary genes.