Subfunctionalization

Subfunctionalization was proposed by Stoltzfus (1999) and Force et al. (1999) as one of the possible outcomes of functional divergence that occurs after a gene duplication event, in which pairs of genes that originate from duplication, or paralogs, take on separate functions. Subfunctionalization is a neutral mutation process; meaning that no new adaptations are formed. During the process of gene duplication paralogs simply undergo a division of labor by retaining different parts (subfunctions) of their original ancestral function. This partitioning event occurs because of segmental gene silencing leading to the formation of paralogs that are no longer duplicates, because each gene only retains a single function. It is important to note that the ancestral gene was capable of performing both functions and the descendant duplicate genes can now only perform one of the original ancestral functions.

Subfunctionalization after gene duplication is thought to be the newer model of functional divergence. Before 1910, scientists were unaware that genes were capable of multifunctionalization. The original thought was that each gene possessed one function, but in fact genes have independently mutable regions and possessed the ability to subfunctionalize.Neofunctionalization, where one paralogous copy derives a new function after gene duplication, is thought to be the classical model of functional divergence. Nevertheless, because of its neutral mutation process subfunctionalization seem to present a more parsimonious explanation for the retention of duplicates in a genome.

Specialization is a unique model of subfunctionalization, in which paralogs divide into various areas of specialty rather than function. In this model both gene copies perform exactly the same ancestral function. For instance, while the ancestral gene may have performed its function in all tissues, developmental stage, and environmental conditions, the paralogous genes become specialists, dividing themselves among different tissues, developmental stages, and environmental conditions. For example, if the ancestral gene is responsible for both digestive and lymphatic regulatory processes, after gene duplication one of the paralogs would claim responsibility for lymphatic regulation and the other for digestive regulation. Specialization is also unique in the fact that it is a positive rather than neutral mutation process. When a gene specializes among different tissues, developmental stages, or environmental conditions it acquires an improvement in function. Isozymes are a good example of this because they are gene products of paralogs that catalyze the same biochemical reaction. However, different members have evolved particular adaptations to different tissues or different developmental stages that enhance the physiological fine-tuning of the cell.

...
Wikipedia