A mutation is a change to the DNA sequence of a gene, and is permanent. They can occur in somatic (body) cells or gametic (gamete) cells. A mutation that occurs during the production of a gamete is inheritable. A mutation in a somatic cell is not inheritable.
Mutations result from a mistake being made during DNA replication. Remember that DNA replication happens before any type of cell division - so any time new cells are made (mitosis/meiosis) there is a chance that a mutation will be present in them. Mutations are very rare because there are enzymes which 'proof read' the new DNA and correct any mistakes, but sometimes they miss mistakes and they are not corrected. |
The likelihood of mutations occurring increases with exposure to mutagens. Mutagen can be things like radiation, viruses, chemicals, diet and alcohol, and increase the likelihood or chance of mutations happening. Mutagens result in different genotypes and phenotypes being produced as mutations occur, changing the DNA sequence. |
Asbestos, tobacco, benzines and vinyl chlorides are mutagens. Exposure to these chemicals may cause cancer |
There are two main types of mutations
Point mutations & frameshift mutations
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Point mutation
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Frameshift mutation
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Other types
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Point mutation (aka. substitution mutation)
A point/substitution mutation is when one nucleotide is swapped out and replaced by a different nucleotide. Sometimes more than one nucleotide can be substituted. Point mutations do not change the number of nucleotides in a gene, therefore there is no frameshift.
Point mutations may result in one codon changing - resulting in a different amino acid being coded for. However, the mutation may not code for a different amino acid because of redundancy due to degeneracy, meaning the mutation may have no effect on the polypeptide chain. |
Depending on the effect a mutation has, it can be given a particular name...
Samesense
When a mutation does not cause a change in the amino acid (redundancy) - meaning the amino acid sequence remains same, meaning the protein remains the same! This is also called a silent mutation.
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Missense
When a mutation changes the amino acid in a sequence, the overall function of the protein may or may not be affected (depending on the change). This type of mutation has the potential to produce a big effect.
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Nonsense
When a mutation results in the production of a STOP codon, it will severely impact the protein formed. The polypeptide chain will be terminated earlier than it should be!
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