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Wednesday, 27 March 2013

Mutations and the Human Genone

DNA replicates itself often and very accurately, and there is a checking mechanism in place to help with accuracy.
If a change does happen, we call it a mutation. The rate of change is increased by radiation from the sun’s or other sources’ atomic radiation.
Discuss why most mutations never influence the genome of the population.

Bryony's Response:

DNA replication is very vital to an organism’s survival as it needs to happen for cells to divide. DNA replication is a very complicated process but is also very accurate but sometimes mutations do happen. There are many different types of mutations and many will affect people differently and mutations can be caused by environmental factures such as radiation. But despite all this most mutations do not have an effect on the genome of the human population.   

DNA replication occurs when new cells are created. Before a cell can divide into daughter cells the DNA must be replicated to produce the new chromosomes for the new cells to carry. DNA replication occurs when the body needs to make new cells. DNA replication starts when a cell is preparing to divide. An enzyme called Helicase splits the DNA double helix down the middle separating the two strands of DNA. As the strands unwind an enzyme called gyrase prevents the strands from getting tangled by making temporary nicks in the strands that will be sealed up later. When the two strands are separated several small proteins called single stand binding proteins temporarily bind each side and keep them from re-joining with each other. As the strands unzip the bases become exposed and an enzyme called DNA polymerase III goes down the DNA strands and add new nucleotides to each strand. The nucleotides pair with the complementary nucleotides on the existing strand. But when the double helix is split there is a leading strand and a lagging strand. Because DNA polymerase must move in the 5' to 3' direction on the DNA strand when the enzyme is on the lagging strand the enzyme must move away from the replication fork. The replication fork is the junction point where the strands are being split. If the enzyme moves away from the fork while the fork is uncovering new DNA some DNA will not be replicated. So the lagging strand needs to be replicated in small segments. These fragments are then stitched together by DNA ligase and this creates a full strand of DNA. This shows that DNA replication is a very complicated process that is necessary for cells to divide.
Although DNA replication is extremely accurate sometimes things go wrong and mutations can occur. A mutation is a permanent change in the DNA sequence that makes up a gene. Mutations are caused by DNA replication going wrong.  Every time a human cell divides and its DNA replicates it has to copy and transmit the exact same copy of three billion nucleotides to it daughter cells. Like everything else in the world DNA replication is not always perfect. Sometimes mistakes happen with the polymerase enzymes and they insert the wrong nucleotide or to many or two few nucleotides into a sequence. Fortunately many of these mistakes are fixed by various DNA repair processes and DNA repair enzymes. But some replication errors make it past the repairing enzymes becoming permanent mutations. Mutations can also be caused by environmental factures such as nuclear radiation and ultraviolet light from the sun. Ultraviolet light, nuclear radiation and certain chemicals can damage DNA by altering a nucleotides base so that it seems like another base. So when the DNA replicates the altered base will pair with an incorrect base and cause a mutation. For example an altered guanine base could get pair with a thymine base. This would cause a permanent mutation in the DNA sequence.  Environmental factures especially nuclear radiation can also break the phosphate back bone of DNA that carries a gene. This creates a mutated form of the gene that may produce different proteins. Also cells that have broken DNA will try to fix the broken ends of DNA by joining the loose ends to other pieces of DNA within the cell. This creates a mutation called translocation. If the breakage point is within or near a gene the gene’s function may be altered. This shows how mutations occur and that although they can happen regularly they are not all permanent.    
There are many types of mutations. Mutations can range in size from a single DNA base to a large part of the chromosome. There are three types of mutations germline mutations, de novo mutations and somatic mutations. Germline mutations are present in gametes. This type of mutation is present throughout a person’s life and is in virtually every cell in their body. This type of mutation can be passed down to the next generation and is sometimes called hereditary mutations. De novo mutations only occur in an egg or sperm cell or during fertilization. This mutation well be present throughout the person’s life in very one of their cells but there will be no family history of this mutation. Somatic mutations occur in individual cells at some time during a person’s life. But since these mutations occur in somatic cells which are cells that are not gametes they will not be passed on to other generations. These types of mutations will affect people differently for example a somatic mutation will not be present throughout all of someone’s life unlike a de novo mutation which will be. De novo mutations can be things like mental disorders and birth defects such as heart problems. While a somatic mutation would more likely cause cancer or other diseases. This shows that different types of mutations affect people in different ways. Therefore each mutation can be different and have different effects on someone’s life. But do many mutations affect the overall human population genome.
Most mutations do not affect the genome of the human population because many mutations occur in somatic cells so they don’t get passed on, many mutations occur in noncoding DNA, there are so many humans in the world that one mutation will not really affect the overall genome of the population and if a mutation is extremely bad the person with it will not survive . Mutations that happen in somatic cells will not be passed down to the next generation because they do not occur in gametes so not many humans will carry this mutation because it cannot be inherited. For example a mutation that can be inherited like being left handed will spread throughout the human population more than a mutation that cannot be inherited. Another reason is because about 95% of human DNA is noncoding DNA meaning that it does not code for proteins that are not expressed in the organism’s phenotype. Because a lot of our DNA is noncoding the chances are that mutations will not happen in the coding DNA so they will not have any effect on the person’s genome or the populations. Another reason is because there are simply so many people on the planet that if a mutation occurred in one or two peoples genes it will not make a big difference in the genome of the population because there are millions of people without this mutation and the chances that they will breed with someone with the same mutation is very slim. For example if someone with a mutation breed with someone without the mutation the children may not carry the mutation and the mutation would have to be in the parents gametes to be passed down to the children anyway so the chances of all this happening are very slim. Lastly if a mutation is extremely bad the person carrying it would not be able to survive or would not be able to produce children so the mutation would no get passed on anyway. This shows that many mutations don’t get passed down to other generations that most mutations occur in noncoding DNA and if mutation is really really bad it will not get passed down anyway. Therefore most mutations do not affect the genome of the human population.
Although some mutations to spread through the human population. Mutations that spread through the population are generally mutations in gametes because they can be passed down to other generations. An example of this is not having a hitch hiker’s thumb or being left handed. Both of these mutations can be inherited and have passed through a lot of the population because it’s not extremely odd to find someone who has a straight thumb or who is left handed. So some mutations can affect the human population’s genome. This shows that some mutations can affect the population’s genome but when you think of all the other mutations that will occur in peoples DNA everyday it becomes clear that most mutations must not affect the genome of all the population or the human race would be every mutated and constantly changing characteristic as new mutations occurred.                
To conclude DNA replication is a very accurate process but nothing is perfect and mutations do happen sometimes. Mutations can be caused by environmental factures such as radiation there are many different types of mutation and each type will affect people differently. Most mutation does not affect the genome of the human population because they occur in noncoding DNA and the chances of the being passed on are very thin. I believe that my information is reliable because a lot of it doubled up on different websites and this lead me to believe that the information was correct and the information seemed to be believable. Therefore most mutations do not affect the genome of the human population.

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