Sunday, March 15, 2009
Preventing Mutations
On page 59 Carol lists 4 facts about mutations, that they either "(1) occur in regions of our D?Na that are empty of any meaningful information (2) fall in or near a gene and do not change how that gene works, (3) are compensated for by our carrying two seperate copies of most genes, or, (4) affect the gene in such a way that produces an effect within a tolerable range of variation." My question is, don't almost all of these facts mean that our bodies are designed to prevnt or prolong mutations? If so, what prime conditions, threats, or situations does it truely take for a mutation to "stick", to be benificial? If the "odds of adaptively useful mutations arising are very much on the side of nature," should we create more mutations that could lead to advantages later on in the evolutionary scale?!
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On page 59, Carroll is actually stating why MOST people are unaffected my mutations, and it is because the mutations occur in one of those four situations. There are, however, cases where mutations do in fact change the phenotype of an individual for better or for worse. Looking at this, my answer would be that although our body has many mechanisms to fix or resist mutations, these mechanisms are necessary for the survival of every organism, and it is a necessary trade off for a smaller amount of mutations.
ReplyDeleteAn example of some mechanisms used by our cells to repair mutations during cell division is nucleotide excision repair, or the removal of a misplaced base pair with nuclease and then filling its place with DNA polymerase and sealing the backbone with ligase. The human body does use these mechanisms to defend against mutation, but if it ceased to do so in order to promote mutations that might offer advantages, human beings might be extinct before a beneficial mutation can occur. Under these methods, humans, and other organisms as well, are assured proper reproduction and growth without errors, however there is still the chance that a mutation might occur to give the organism an advantage. In this idea, a beneficial mutation can occur in the same likelihood as a detrimental or useless mutation, but the type of mutation, whether beneficial or useless, determines if it “sticks”. The molecular randomness of mutation and the method in which the mutation is formed doesn’t determine whether the mutation will be retained by a species, but rather the overall phenotypic changes and their effect on the survival of a species. If a mutation helps an organism survive better than another organism without the mutation, the mutant will have increase survival.
Based on this argument, it would seem reasonable that this method of reproduction and growth with very rare mutations seems like the safest method for a species, however speaking theoretically, creating certain mutations in a controlled experiment could be very beneficial to any species that such an experiment is performed on. The reason this does not contradict my previous statement is that purposefully creating very few mutations will not completely destroy the means for survival of the organism. This is because, as stated earlier, the main reason, as one might ask, as to why it is not a selective advantage to have mutations more often, is that there is a trade off between rare mutations and endangering survival of a species. When a mutation occurs, the organism can be endangered, so it is possible that with frequent mutations, yes it is more likely to acquire a beneficial new trait, but it is also more likely to put an organism’s survival at stake. Therefore, while making a species constantly create more mutations would be harmful to their survival, making one mutation in one organism would help accelerate the process of finding beneficial mutations. This is not harmful to a species because it is not interfering with its basic methods of defending itself against errors in replication.
Our bodies are designed to accept mutations to our benefits or our “tolerable range of variation” in other words, our characteristics that make us unique like shape or size. Carroll uses these four facts about mutations to describe the majority of mutations in the human DNA. Humans have many mechanisms to decrease mutations but they also have many events that may cause mutations, such as replication. Many mutations do cause diseases and illnesses, but most mutations cause a tolerable change that causes diversity and variation. These mutations are necessary for natural selection and the survival of many organisms. For instance, in the book Carroll uses the example of mice that blend into their surroundings, but when the environment changes and they no longer can hide in their environment they are targeted easier by predators, but individuals that may blend in better have a natural selection and other time the mice will blend in once again.
ReplyDeleteFor a mutation to “stick”, it depends solely on how useful the gene is that is mutated. Bringing back the mouse example, if the mice have a mutation that makes them lighter and they blend less, natural selection will cause this mutation to easily be removed and not passed down to an offspring. If the mutation is harmless it usually does not “stick”. A beneficial mutation will “stick” because it will allow the organism to reproduce and survive longer. It will be passed down to its offspring.
Creating mutations purposely may be beneficial to an organism, but we would have to ensure that the mutation would be an advantage. One mutation in an organism can help us understand and study mutations; it may also help us study pathways and functions a certain gene is controlling. Purposeful mutations can be very helpful, but must be watched carefully. When Carroll states that the odds are very much on the side of nature, mean that the genes that have advantages and increased survival rates will be passed on and continue to increase over time. Nature will cause an organism to become more convenient and survive longer through natural selection.
http://www.actionbioscience.org/evolution/futuyma.html
http://www.infoplease.com/cig/biology/natural-selection.html