Saturday, March 21, 2009
Fossil Genes Versus Immortal Genes
Carroll classifies fossil genes as those that have evolved "as a consequence of the continuing action of mutation, over time, in the absence of natural selection," (123). Mutations and sexual recombination create variation within the genetic pool of a population. New alleles originate only by mutation and these can be either synonymous or non-synonymous. As a result, some mutations can cause redundancy and others have no significant impact. However, mutations that cause the erosion of genes contribute to fossil genes. With such fossil genes being left behind with the relaxation of natural selection, many "injurious variations," as Darwin would have stated, will become rampant. Are such "junk" fossil genes truly "injurious" if they (can) create new alleles over time? Are fossil genes only eroding away just as Carroll states? Is it possible to have a once functional gene become a fossil gene, and then the same fossil gene becomes new gene that has either an injurious or a beneficial effect? What if immortal genes became fossil genes-why or why can't it happen? Could fossil genes contribute to the creation, through mutations, of "new" immortal genes to last through future generations? Carroll uses the phrase "Use it or lose it." How does this affect immortal versus fossil genes as well as your response(s) to the previous questions? I urge responders to read Carroll 123 carefully as well as Campbell 454.
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[Are such "junk" fossil genes truly "injurious" if they (can) create new alleles over time?]
ReplyDeleteFirst of all, fossil genes aren't actually injurious to an organism. The gene eventually fossilized because it wasn't needed: if the mutations that first affected the gene were injurious, natural selection would kill off the mutant.
Since mutations can do pretty much anything to an organism, a fossil gene could possibly be revived as something new. However, as long as the organism never really needs the gene any longer, harmful changes will be lost thru natural selection, but beneficial mutations would probably remain.
[What if immortal genes became fossil genes-why or why can't it happen?]
Immortal genes are essential to life for many organisms. These genes couldn't possibly fossilize, because a mutation that renders one useless would kill the organism.
[Could fossil genes contribute to the creation, through mutations, of "new" immortal genes to last through future generations?]
Organisms with fossilizing genes face very little selective pressure, so I doubt mutations could possibly need to genes necessary for survival. These organisms have more than enough to survive due to the lack of pressure. They don't need to adapt to anything, so I doubt that even minor beneficial mutations will be passed down.