Page "Pseudogene" Paragraph 9

# Disabled genes, or unitary pseudogenes.

Various mutations can stop a gene from being successfully transcribed or translated, and a gene may become nonfunctional or deactivated if such a mutation becomes fixed in the population.

This is the same mechanism by which non-processed genes become deactivated, but the difference in this case is that the gene was not duplicated before becoming disabled.

Normally, such gene deactivation would be unlikely to become fixed in a population, but various population effects, such as genetic drift, a population bottleneck, or in some cases, natural selection, can lead to fixation.

The classic example of a unitary pseudogene is the gene that presumably coded the enzyme L-gulono-γ-lactone oxidase ( GULO ) in primates.

In all mammals studied besides primates ( except guinea pigs ), GULO aids in the biosynthesis of Ascorbic acid ( vitamin C ), but it exists as a disabled gene ( GULOP ) in humans and other primates.

Another interesting and more recent example of a disabled gene, which links the deactivation of the caspase 12 gene ( through a nonsense mutation ) to positive selection in humans.