On page 57, Sean Carroll explains the importance of mutations in evolution. Discuss differences between mutaion and natural selections and how they affect the process of evolution. Give some examples of each process ( not from the book) Discuss how mutation and natural selection occurs and explain why we have misconseptions about mutation that all mutaions are bad. You may need to discuss the process of making DNA, RNA and proteins and the relationship between structure and function and fianlly, explain how this relates to survival and evolution.
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A mutation and natural selection are two completely different things. A mutation is a variation in the gene (by insertion, deletion, repetition, etc. of base pairs) that changes the gene’s function. The gene will code for a different protein, which will perform a different function, for better or worse. Mutations happen completely by chance. Natural selection decides which mutations stay and which mutations go.
ReplyDeleteA mutation occurs when the DNA code is changed in such a way as to change its code. The last part is important because sometimes a change in base pair sequence will still code for the same protein; this is due to the fact that most proteins can be created by multiple triplets (codons). For example, TTA and TTG both make leucine. In that case, the change would not be a mutation. A mutation would have to be when the protein being produced is changed due to a change in DNA sequence. An example of a mutation would be sickle-cell disease. It is caused by a mutation of a single base pair in the gene that codes for hemoglobin. The change of a single nucleotide in the DNA’s template strand lead to the production of an abnormal protein, altering the hemoglobin and producing the disease. This is why many people associate mutations with negativity; they change the sequence of DNA, so they must be harmful. They cause disease, disability, and mental retardation. They mess up the order of things. If the DNA sequence works for everyone else, then a change in the sequence can only be harmful, right? Wrong. Mutations can be beneficial. A mutation in the green algae Chlamydomonas ensured that it would be able to grow in the dark.
Mutations don’t just take over an entire species overnight; it happens gradually. This is where natural selection comes in. The Chlamydomonas mutation only spread over the entire population after 600 generations. Generally what happens is this. If a mutation is, by chance, beneficial to an animal, then that animal will have a higher chance of living longer and finding a strong mate. That animal will probably reproduce and pass on the mutation to its offspring. Its offspring will have an advantage over other animals of the same species, and those offspring will grow to be older, stronger, and more fit for reproduction. Over time, if the mutation is at all beneficial, it will spread over the entire environment because of natural selection. If the mutation is harmful, it will die out eventually due to the animals’ decreased chance of reproduction with that mutation. In evolution, only the strong survive. Mutations make animals stronger and natural selection spreads the gene to entire species.
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ReplyDeleteMutations and natural selection are two aspects that work hand in hand in allowing the other to work successfully. Natural selection may be more particular while mutations are random but both are forms in allowing for a species to evolve and adapt to their surroundings for a higher survival and reproduction rate.
ReplyDeleteA mutation may occur in a gene when cell division occurs or when DNA is copied for meiosis or mitosis. The basic components of DNA are the nitrogenous bases Arginine(A),Thymine(T), Guanine(G) and Cytosine(C). By placing these 4 letters in different patterns for different lengths, genes are created and can be encoded to create proteins that work in the body to carry out the most simple to the most complex tasks. When a mutation occurs, a letter or group of letters can be inserted, removed, or switched, causing the entire code or a segment of the code to be changed and altered. This effect can both be good or bad, a mutation giving new proteins that allow for a more efficient body or a mutation that may cause miscarriage or death. These mutations can be placed into categories. When a single base or letter is substituted there are 4 different types of mutations that may have occurred. The first is a missense mutation in which a single base is substituted for another and in turn causes a new amino acid to be coded for. This can be seen in sickle cell anemia when the code is slightly altered changing the 6th amino acid from glutamic acid to valine. From what appears to be a simple change greatly affects the health of the person. The second type of mutation that may occur is the nonsense mutation in which a base is switched causing a code for an amino acid to be changed into a stop codon. This stop codon causes the mRNA transcription to stop early and is the cause for diseases such as cystic fibrosis and duchenne muscular dystrophy. The third mutation that may occur is the silent mutation. In this mutation a base is switched but there is no change in the end result. This is because there are multiple codons that code for a single protein. In this way a mutation has a less likeliness to change the amino acid that is coded for. This mutation can only be spotted by sequencing the gene and seeing where this change has occurred. The fourth mutation is splice site mutation. At certain places an enzyme must come in and remove introns that are not used in coding for proteins. If this splice site is changed by the substitution of a base the intron will not be properly removed causing a useless protein to be created.
There are also insertions and deletions where a letter or group of letters may be added or deleted from DNA. This can be fatal because if groups of 3 are not inserted the new code pairs may cause a shift in the genes that creates differing groups of threes for each amino acid leaving almost the entire strand useless. If a group of 3 is inserted there may be repeats and this can cause diseases such as Huntington's disease in which the codon 'cag' is repeated.
There are three kinds of mutations, germ line mutations, de novo (new) mutations, and somatic (acquired) mutations. Germ line mutations are those mutations that are hereditary and are passed on to offspring through parents. The egg and sperm carry this mutation and the person will have the mutation for their entire life time. De novo mutation occurs right after fertilization. This is an explanation for a genetic disorder from mutation that is not present in the family history but has only just popped up. Somatic mutations are those mutations which occur in a single cell of the person after birth. These can be caused by things in the surrounding environment. Examples of this would be ultraviolet light from the sun. Somatic mutations may also occur when a cell is going through mitosis and DNA is coded improperly. These somatic mutations do not normally affect the egg or sperm cells and so are not passed on through generations.
Mutations are normally seen as bad because they are in correlation with such diseases as named above. This is for many people the only way in which mutations are known. Much of the population is unknowing to the fact that certain mutations have occurred in history that allow for our body to produce new proteins that enhance certain aspects. For example in hemoglobin 2beta and 2 alpha chains are used in binding oxygen in order to distribute it among the vital organs. It can be seen that on the chromosomes there are multiple sites where hemoglobin can be coded for. There is also a gamma chain that seems to be very closely related to the beta chain. This alteration most likely came from mutation and allows the hemoglobin to more efficiently bind to oxygen and is used by the fetus. The hemoglobin of the fetus has 2 alpha chains and 2 gamma chains while the fetus must share its oxygen with the mother. Right before birth the coding for the gamma chain is stopped and the coding for the beta chain is started allowing the hemoglobin to then have 2 beta and 2 alpha chains.
Natural selection can come into play after a mutation has occurred. In natural selection there may be a characteristic resulting from a mutation that allows for the organism to have a higher likeliness to survive and reproduce. With mating, this new characteristic that is encoded in the genes of the organism will most likely be passed down to its offspring. In the chance that it is, these offspring will then too have this characteristic, which allows it to have a higher rate of survival. Through natural selection this characteristic will eventually become dominant. This can be seen with the increasing number of offspring with this characteristic because the parents will survive due to this characteristic. Also those that do NOT have this characteristic are more likely to not survive and reproduce and so will have fewer offspring that are lacking in this certain characteristic. This can be seen in a simple characteristic of fur color for the mice that are mentioned in the book on pages 61 - 62. The rock pocket mice are found living in areas with dark lava rock. In this way the dark fur is an advantage in correlation with camouflage from predators. Those mice with dark fur are more likely to avoid predators and survive and reproduce while the lighter fur mice are more likely to be killed by these predators and have a declining rate of survival and reproduction. The time length for natural selection to occur will be based on certain aspects such as lifespan, number of offspring, and selective advantage of that certain characteristic. The formula for this rat can be found on page 61.
Mutations and natural selection come hand in hand. As a mutation occurs it can hold a selective advantage and through the process of natural selection this mutation becomes a dominant trait in the species. They work in unison such as in the rock pocket mice in which a mutation for the black fur coat was first made. Then with this mutation natural selection occurred in spreading this characteristic in order to increase survival and reproduction rates. By working together mutations and natural selection are thee basis for evolution and adaptations.
http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/genemutation
http://wiki.answers.com/Q/How_do_gene_mutations_occur
http://www.ebi.ac.uk/2can/disease/genes5.html
http://www.newton.dep.anl.gov/askasci/mole00/mole00468.htm
http://en.wikipedia.org/wiki/Natural_selection