What is it called when one gene has an impact on the expression of another gene?

The correct answer is that when one gene has an impact on the expression of another gene, this phenomenon is known as epistasis. Epistasis occurs when the effects of one gene are masked or modified by one or more other genes, leading to alterations in the expected phenotypic outcome.

For instance, if gene A influences the overall color of a flower, but gene B determines whether or not that color can be expressed, the interaction between these two genes exemplifies epistasis. The expression of gene B can prevent the effects of gene A from being seen in the phenotype, showcasing the intricate relationships between genes in determining traits.

Understanding epistasis is crucial in genetics as it demonstrates that multiple genes can interact in complex ways, shaping the characteristics we observe in organisms beyond simple dominant-recessive patterns.