Subfunctionalization

[8][7] During the process of gene duplication paralogs simply undergo a division of labor by retaining different parts (subfunctions) of their original ancestral function.

[11] Nevertheless, because of its neutral mutation process subfunctionalization seem to present a more parsimonious explanation for the retention of duplicates in a genome.

[7] When a gene specializes among different tissues, developmental stages, or environmental conditions it acquires an improvement in function.

[14] However, different members have evolved particular adaptations to different tissues or different developmental stages that enhance the physiological fine-tuning of the cell.

Gene sharing is a fairly common occurrence and is most often seen in enzymes taking on a various subfunctions such as signal transduction and transcriptional regulation.

[7] The most noteworthy example of gene sharing is crystallins, the proteins responsible for transparency and diffraction in the eye lens, which have also been found to serve as a metabolic enzyme in other tissue.

[15] In the Duplication- Degeneration- Complementation (DDC) model of subfunctionalization both gene copies are needed to perform the original ancestral function.

[10] In this model after a duplication event, both paralogs suffer deleterious mutations leading to functional degradation.

[7] One example of the DDC model is when functionally similar paralogs are expressed at such low levels that both copies are required to produce sufficient amounts of the original gene product.

[7] Segregation avoidance occurs when an unequal crossing over event leads to a locus duplication containing two heterogeneous alleles creating a situation akin to permanent heterozygosity.

The unequal crossing over and subsequent duplication of a locus containing heterogeneous alleles ensures the highest possible fitness.