Pseudogene
Pseudogenes are genes present in an organism's genome that have lost the ability to code for proteins due to mutation. [1] They were first identified and dubbed in the late 1970s when researchers began finding non-coding regions in some organisms that were similar to actual coding genes in other organisms. [2] So far an estimated 19,000 pseudogenes have been identified in the human genome, this is almost equal to the total number of coding genes (21,000). [2] Humans have many pseudogenes including L-gulonolactone oxidase which is used to synthesize vitamin c. Research reports that this gene was inactivated in the common ancestor of all simians. [3]
Finding pseudogenes
Pseudogenes are often difficult to parse from the large amount of non-coding base pairs in the genome. Convention requires two elements to be present to label a sequence a pseudogene. The first is homology which is the requirement that a sequence be demonstrated to descend from a functional copy of the gene and the second is non-functionality which is the requirement that the gene not code for a protein in the organism in question. [2]
Pseudogenes and neutral selection theory
Because pseudogenes do not code for a function many scientist have hypothesized that the accumulation of mutations would not be constrained by selection pressures.[1] This is known as neutral selection, and pseudogenes have been studied extensively to test various theories of neutral selection. [4] It has been determined that mutations fixate in pseudogene regions at about 30 percent higher than in coding regions of DNA. [4] Some theorist have argued that there maybe some selection pressure on pseudogenes (such as on genome size in general) so conclusions should be tempered.[1] Others have determined that base pair mutations are not completely random, favoring accumulation of guanin and cytosine. [4] Despite these findings research on pseudogenes still continues to be a productive avenue for exploring mutation and selection.
Creationist Perspective
Creationist scientists assert that pseudogene analysis used to argue to validity of the theory of evolution is invalid. [5][6]
Evolutionary Perspective
Pseudogenes have been identified in a wide range of organisms from bacteria to mice to humans, the total number of pseudogenes in a given genome is not predictable but specific pseudogenes are often compared across species to assert complex evolutionary relationships [2]
See also
References
- ↑ 1.0 1.1 1.2 Petrov, D.A, Hartl, D.L. (2000). Pseudogene evolution and natural selection for a compact genome. The American Genetic Association 91:221-227. [1]
- ↑ 2.0 2.1 2.2 2.3 Gerstein, M, Zheng, D. (2006). The real life of pseudogenes. Scientific American 95:48-55. [2]
- ↑ http://www.cast.uark.edu/local/icaes/conferences/wburg/posters/kmilton/kmilton.html
- ↑ 4.0 4.1 4.2 Bustamante, C, Neilsen R, Hartl, D. (2002). A maximum likelihood method for analyzing pseudogene evolution: implications for silent site evolution in humans and rodents. 19:110-117. [3]
- ↑ http://www.answersingenesis.org/tj/v14/i3/pseudogenes.asp
- ↑ http://www.answersingenesis.org/tj/v14/i3/pseudogenes_genomes.asp