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Types of Gene Mutations
Since we're talking about mutations, it is necessary for us to understand how mutations are classified. Mutations that occur under natural conditions without the action or effect of an external agent are called spontaneous mutations. For example, bacteria, archae, and eukaryotic microbes produce roughly one mutation per 300 chromosome replications. The other type of mutation is an Induced mutation, which, as the name suggests, involves the role of external agent.
Classification of Mutations:
A silent mutation does not alter the message or the protein sequence of the gene/DNA and therefore considered to be a 'silent' mutation, as there is no no final effect.
A substitution mutation involves a change in the DNA sequence, which eventually leads to changes in the amino acid sequence where one amino acid is replaced for another. Hence the name substitution mutation.
As the name suggests, deletion mutation involves deletion of part of a chromosome or a few bases from the DNA sequence. This type of mutation is severe and is also evolutionarily significant as this can be used to trace the phylogeny of organisms.
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More on Mutations
A mutation that introduces and stops codon in the sequence which ultimately prevents the formation of the gene product is called a nonsense mutation. This type of mutation is usually serious and is involved in the loss of function mutation associated diseases.
An insertion mutation involves the introduction of additional DNA into the DNA sequence. This type of mutation is also considered dangerous, as it can alter the reading frame of the gene sequence and thereby creating or resulting in the loss of the protein product.
A point mutation is a name given to a muation that involves just one base of the DNA sequence. A point could be substitution mutation or a deletion mutation, implying that either one base is substituted or removed respectively.
Any mutation that results in the altering of the reading frame of a protein is called as a frame shift mutation. Usually a insertion or deletion mutation turns out to be a frameshift mutation. Most frameshift mutations result in harming the protein product by either completely preventing it from forming properly or resulting in a malformed or inactive form.
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Mutations are Agents of Evolution
In sum, mutations cannot be considered to be completely harmful across the board. They are also considered to be agents of evolution by allowing cells that change in accordance to their surroundings to thrive. There are quite a few examples of these instances. For instance, take a subpopulation of people who do not carry the receptor required for the binding of HIV and are therefore resistant to its infection. Such a mutation would allow these phenotypes to survive more. It is also significant in infection studies, since a virus that can mutate its protein coat will not recognised by the immune system and therefore would infect with more vigor. In the upcoming era of the personal genome studies, such personalised genotypes would help us build a profile of the disease risks that are probable to each and every individual and potentially to increase life span.