Refer to page 72. "...two key elements of the evolutionary process -- the power of natural selection to preserve the DNA record and the descent of life from common ancestors."
Why is it important to maintain a fossil record of DNA? Why is fossil DNA present? Is it biologically important, aside from the fact that it's helpful for biologists to see what genes we have had and scientifically deduce the importance of these genes and the reason for their presence beforehand? Basically, is it biologically important when you don't think about people actually researching it? How is it important for our bodies?
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Well first I don't think that he was saying that we have a fossil record of pasts DNA in humans, but that our DNA, the current DNA in our body, shows the history of DNA natural selection and mutation. Our DNA today can be compared to future DNA and past DNA in order to trace evolution. It is biologically important to preserve our DNA records in our body because that is what is passed down to our children. Therefore, only the genes that are present in our DNA record will be passed down because those are the genes that we have naturally selected. These genes are therefore favorable in our environment because they have lasted many generations and have been passed down without being mutated. Many of the genes that we have in our DNA record today are immortal genes because they have not been affected by mutations because they are necessary for our survival and ability to reproduce. In addition, the fossil record tells our bodies what to continue to pass down to our children based on if it has been an advantage in the past. Yes the DNA records are extremely useful to biologists who wish to trace our evolution, but those records are also vital to our body functioning properly because through evolution and natural selection our body has decided that the DNA in our record is necessary for our survival.
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ReplyDeleteThe fact is that it is impossible to say whether it is "important" or not to maintain the fossil genes within our genome. The fact that they're there only indicates that random mutations over time have not yet totally removed them from our DNA.
ReplyDeleteThat being said, from a strictly biological point of view, these genes are no longer necessary for our survival or reproduction. This is the reason why they have fallen into disrepair. Over the course of time, the proteins that each gene coded for and the trait that each protein led to were no longer under strict selection.
An important example that Carroll describes in his book is the loss of full color vision in nocturnal mammals. Full color vision requires three proteins known as opsins. These opsins are named SWS, MWS, and LWS. SWS is tuned to blue light, MWS is tuned to green light, and LWS is tuned to red light (Carroll 95). For the lifestyles of nocturnal mammals, the ability to see the whole color spectrum is dispensable. Because the trait is dispensable, the gene that codes for it is allowed to accumulate mutations. In the owl monkey, a nocturnal primate, this is seen to be the case. Sixty base pairs into its SWS gene, a mutation has changed "TGG" to "TGA," a stop codon. This results in a much shorter, nonfunctional protein (124). Additional analysis of the DNA of nocturnal prosimians (lemurs, bush babies, lorises) reveals that their SWS genes are all missing big chunks of code near the beginning. This results in a nonfunctional protein. The blind mole rat, another mammal that lives in the dark, also has a SWS gene that is highly degenerated. All of these examples suggest that at one time, the evolutionary ancestors of these mammals had the ability to see in full color. Over the course of time, the ability was lost, but the remains of the SWS gene remain. That is why the SWS gene is a fossil gene. It exists in part, but no longer has a biological function.
Of course, from a scientific and research point of view, these "fossil genes" are essential pieces of evidence of evolution. As in the example of the nocturnal mammals above, these fossil genes help to indicate that they evolved from animals that saw in full color and eventually lost that ability. This is powerful evidence of evolution and it is also one of the major examples that Carroll uses in his book.
Info on opsin genes from Carroll 95
Info on nocturnal mammals from Carroll 124-6