subfunctionalization

Subfunctionalization is an evolutionary process in which duplicated genes, or paralogs, partition the ancestral gene's functions between them. After a gene duplicates, complementary degenerative mutations in regulatory regions or in functional domains can cause each copy to lose a subset of the original functions, so that together the two copies retain the full set of ancestral activities. This idea is encapsulated in the duplication–degeneration–complementation (DDC) model proposed by Force and colleagues in 1999, which posits that selection can preserve both copies because their combined function equals the original gene’s function.

Mechanistically, subfunctionalization often manifests as partitioning of expression patterns—different paralogs become active in different tissues, developmental stages, or environmental conditions—and/or partitioning of biochemical activities, such as substrate specificity or protein–protein interactions. The result is that neither copy alone is fully equivalent to the ancestral gene, yet both contribute to fitness.

Evidence for subfunctionalization comes from comparative genomics and functional studies showing divergent expression and complementary loss-of-function phenotypes among paralogs in diverse organisms, including yeast, plants, and animals. It is frequently contrasted with neofunctionalization, in which one copy gains a new function, though both processes can occur sequentially or concurrently. Dosage balance constraints and network architecture can also influence the retention of duplicates.

In summary, subfunctionalization provides a framework for understanding how gene duplicates are maintained and how gene regulatory networks evolve through partitioned functions.