Phenocopy

Phenocopy is a term used in genetics to describe a phenotype that resembles a genetic trait but is produced by environmental factors rather than by the organism’s genotype. In a phenocopy, the outward appearance of the trait matches what might be expected from a specific gene, yet the underlying cause is non-genetic, such as developmental conditions or environmental exposures.

Causes and mechanisms include exposure to teratogens during development, nutritional deficiencies, infections, or other environmental stresses that alter development in ways that mimic inherited conditions. Epigenetic modifications or stochastic developmental factors can also contribute to phenocopies. The concept is relevant across human, plant, and animal genetics.

Examples commonly cited include thalidomide-induced limb defects that resemble congenital limb malformations caused by genetic mutations, or fetal alcohol syndrome, which can mimic certain neurodevelopmental genetic disorders. Maternal infections or teratogenic exposures can yield congenital anomalies that resemble hereditary syndromes, complicating attempts to infer inheritance patterns from families.

Phenocopy has important implications for genetic studies and clinical practice. It can confound linkage and segregation analyses by introducing individuals who express a trait without carrying the causal mutation. Recognizing phenocopies helps prevent misinterpretation of inheritance, underscores the role of the environment in phenotype expression, and informs diagnostic and counseling decisions.