neofunctionalization

Neofunctionalization is an evolutionary process in which a duplicate copy of a gene acquires a novel function that was not present in the ancestral gene. It typically follows gene duplication, an event that produces paralogs. One copy often retains the original function while the other is freed from identical selective constraints and may accumulate mutations that alter its coding sequence or regulatory elements. Through changes in enzyme activity, substrate specificity, expression pattern, or tissue distribution, the duplicate can become functionally distinct, contributing to evolutionary innovation. The concept was proposed by Susumu Ohno in 1970 as a major mechanism by which genomes gain new capabilities.

Neofunctionalization is contrasted with subfunctionalization, where duplicated genes split the ancestral roles between them rather than one gaining a new function. A related concept, the duplication–degeneration–complementation model, emphasizes complementary loss of parts of the ancestral function rather than the acquisition of novelty.

Detection and significance: Neofunctionalization is inferred when a paralog shows a novel function or expression pattern not explained by the ancestral gene, with phylogenetic and functional analyses indicating divergence after duplication. It can be driven by positive selection in the new function, though early changes may be neutral or only weakly deleterious before refinement.

Examples and prevalence: neofunctionalization is observed across many lineages, including plants and animals, and is thought to underlie diversification of metabolic pathways, regulatory networks, and sensory systems. Nonetheless, many duplicated genes are lost or become pseudogenes rather than acquiring a new function.