Pseudogene
From Freepedia
A pseudogene is a nucleotide sequence that is part of the genome of an organism that appears to code for a gene product (typically a protein) but does not (or no longer does so).
Several scenarios have been proposed under which a pseudogene might arise:
- A gene may "die" during evolution if the selective pressure for its function is removed. For example, the environment in which a species lives could change such that the gene product is no longer necessary, or even harmful. Deactivating mutations in the gene would then no longer be selected against.
- A gene duplication event may mean that a genome has two copies of a gene when it only requires one. Deactivating mutations in one copy of the gene would then not be selected against.
- Fragments of the mRNA transcript of a gene may be spontaneously reverse transcribed and inserted into chromosomal DNA.
Pseudogenes can complicate molecular genetic studies. For example, a researcher who wants to amplify a gene by PCR may simultaneously amplify a pseudogene that shares similar sequences. Similarly, pseudogenes are sometimes annotated as genes in genome sequences.
In some cases, the definition of "pseudogene" can become cloudy. For example, Hirotsune et al (2003) discovered a sequence that appeared to be a pseudogene in the sense that it did not code for a protein sequence, in contrast to a homologous gene that did code for a functional protein. However, the pseudogene is expressed and its RNA transcript regulates the activity of the homologous gene. Thus, with respect to protein-coding ability, this sequence is a pseudogene, but in a sense it is a functional non-coding RNA gene.
References
- Hirotsune S, Yoshida N, Chen A, Garrett L, Sugiyama F, Takahashi S, Yagami K, Wynshaw-Boris A, Yoshiki A. (2003), "An expressed pseudogene regulates the messenger-RNA stability of its homologous coding gene.", Nature, 423:91-96. (A functional pseudogene.) In PubMed
