Complementation

Complementation refers to the biological phenomenon where two or more genes, or different mutations within the same gene, cooperate to produce a normal, functional phenotype. This typically occurs when mutations occur in different genes involved in the same biological pathway, or where mutations in different regions of the same gene somehow compensate for each other. It signifies that the mutated genes or alleles are not in the same functional group and can rescue a defective trait when combined. This process is essential for understanding gene interactions and metabolic pathways in various organisms.

Complementation meaning with examples

• In a classic genetic experiment, two strains of yeast, each with a mutation preventing tryptophan synthesis, were crossed. The resulting diploid organism, containing one copy of each mutated gene, *complemented* the mutations. Since the mutations affected different genes, the diploid could now produce tryptophan, demonstrating the functional relationship between the genes and normal phenotype.
• Researchers identified two mutations in Drosophila, one in the 'wingless' gene and another in a separate gene involved in wing development. Crossing flies carrying these mutations resulted in normal wing formation because the mutations *complemented* each other, as their underlying defects impacted different aspects of the development process, leading to a functional outcome.
• A scientist studying a metabolic pathway found two bacterial mutants, each unable to produce a specific nutrient. By mixing both mutants, they observed the production of the nutrient, proving that the mutations *complemented* each other. The two different genes were not in the same functional group, so each can still perform their respective functions.
• In a study on disease resistance in plants, two different resistant genes, when introgressed into a susceptible plant, together provided a higher level of disease protection. The two genes *complemented* each other, leading to more robust disease resistance compared to the presence of each gene individually, demonstrating the interaction between these resistance mechanisms.