Non-complementation

Non-complementation refers to the phenomenon in genetics and related fields where two or more mutations, each individually causing a specific phenotype (observable characteristic), fail to "complement" each other when present together in the same organism or cell. In other words, the combined effect of the mutations results in a phenotype that is distinct from what would be expected if the mutations were in different genes, or a more severe phenotype than either mutation alone, or no observable change. This indicates that the mutated genes are involved in the same or overlapping biological pathways, or encode proteins that interact directly or indirectly, and that both must be functional for a normal outcome. Non-complementation is a crucial concept in understanding gene function, epistatic relationships, and genetic interactions. It's a cornerstone of understanding gene regulation and pathway construction.

Non-complementation meaning with examples

• In yeast, two mutations, *mutA* and *mutB*, both disrupt a metabolic pathway. Individually, each mutation slightly reduces growth rate. However, when *mutA* and *mutB* are combined, growth is severely impaired, demonstrating non-complementation. The genes are involved in related functions and one mutation affects how the other functions.
• A scientist is investigating two mutations which cause an embryo to have abnormal growth in a specific structure. If, when combined in a single cell, the mutations lead to either a more extreme or no growth the mutations show non-complementation. Indicating a genetic relationship in that the mutation directly effect each other's expression.
• Researchers study two bacterial strains, each unable to produce a specific amino acid. If the strains are co-cultured and they cannot mutually support growth, a Non-complementation pattern is observed. This suggests that both genes encode enzymes in the same amino acid biosynthetic pathway and are interdependent.
• A geneticist observes that two mutations, affecting the same protein in slightly different areas, fail to show normal protein function when co-expressed in a single cell. If Non-complementation is found, the mutations have disrupted the same protein's function or that of an interacting protein.