Monday, March 8, 2010
"Dead" Genes
Coyne explains that there is evidence of evolution in every organism's genome. "Dead" genes are genes that "once were useful but are no longer intact or expressed" (Coyne 67). These "dead" genes are not the only non-coding portion of DNA. Introns are sections of DNA that are transcribed to pre-mRNA and then spliced out during RNA editing. However, recent research suggests introns may actually serve an integral part of transcribing RNAi. How does this act as further evidence of evolution within DNA?
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The presence of "dead" genes greatly supports the theory of natural selection and evolution. According to Jerry Coyne, "...the idea that all species were created from scratch predicts that no such genes would exist, since there would be no common ancestor in which those genes were active." (67) Therefore, intelligent design cannot explain why we see vestigial genes in many species. According to Robert W. Meredith, one example of a species with a vestigial gene is that of the dwarf sperm whale. The dwarf sperm whale has teeth that lack enamel. They do however possess the gene ENAM which codes for enamel. Also, fossil evidence suggests that their ancestors did indeed have the gene ENAM and tooth enamel. This evidence suggests that this is a case of vesitgial genes because the whales no longer have tooth enamel, yet they still have the ENAM gene. This gene is now a piece of non-coding mRNA. According to Petro Yakovchuk in his journal article: "B2 RNA and Alu RNA repress transcription by disrupting contacts between RNA polymerase II and promoter DNA within assembled complexes." non-coding mRNA serves a function in regulating transcription. Transcription, as we know, is the process in which RNA is synthesized using a DNA template. This mRNA is then used during translation, during which the proteins coded for in the genes are produced. Therefore, these "dead" genes are actually an incredible tool as they give us hints to the organism's evolutionary past, and they play a role in regulating transcription.
ReplyDeleteCoyne mentions that the genes contained within a genome yet that doesn't function is considered a pseudogene. This is due to the hypothesis made by evolutionists from observations of atavisms and vestigal traits that a no longer used trait doesn't disappear from the genome. Rather, evolution inactivates the gene.
ReplyDeleteThis idea supports evolution in the aspect that if all species were created from an intelligent designer, who had created all species possibly at the same time, dead genes would not be contained within the genome of a particular species. Since it is believed by evolutionists that all species originate from a common ancestor, it is very possible that through the course of evolution, genes that no longer proved useful to a certain species would be rendered inactive over a long period of time, in order to improve the survival of that species. Coyne states that almost every species observed have pseudogenes, including humans.
The most well known human pseudogene is GLO. In species that this gene is active, this gene produces an enzyme known as L-gulono-y-lactone oxidase, which makes vitamin c from glucose. Other animals that also have this pseudogene have the same nucleotide missing from the DNA sequence. Since vitamin C was already abundant in such animals such as primates, fruit bats, and guinea pigs, the inactivation of this gene through a mutation was in no means detrimental to survival. In fact, evolution predicts that this favored species because a protein was no longer necessary, a protein that could have cost many resources to create.
In terms of introns, which are genes that are spliced out during RNA splicing, these genes are spliced because they are not translated into proteins. The IE hypothesis regarding the reason for introns, which are likely pseudogenes themselves, states that original prokaryotic and eukaryotic organisms had introns. However, the prokaryotic ones lost their introns through evolution, obtaining a higher growth efficiency, leading to the absence of introns in prokaryotic organisms.
Another theory, the IL hypothesis, suggests that introns were added after the divergence of eukaryotic and prokaryotic cells into the eukaryotic cells. This hypothesis says that transposable elements, or moveable DNA within a genome, was the origination of introns.
However, development of introns is still being largely debated as there is no clear evolutionary advantage of possessing them. If there is an innate evolutionary advantage, it would make sense why they are within eukaryotic genomes but a clear reason is still unknown.
Sources:
Why Evoution is True
http://en.wikipedia.org/wiki/Intron