Gene or point mutation
The gene mutations are those that alter the sequence of nucleotides of a single gene, so also called point. They can be produced by:
- Base pair substitution: For example, instead of a thymine nucleotide there is a cytosine nucleotide.
- Loss of nucleotides.
- Insertion of new nucleotides.
- Nucleotide inversion.
- Translocation of complementary nucleotide pairs.
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Substitution of bases
They are produced when one nitrogen base changes in one position for another (it is the nitrogenous bases that distinguish the nucleotides of a chain). They account for about 20% of gene mutations. They can be of two types:
- Transitions When a puric base is substituted for another puric one (adenine for guanine and vice versa) or a pyrimidine for another pyrimidine (cytosine for thymine and vice versa).
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- Transversions. When a puric base is substituted for another pyrimidine, or vice versa.
These mutations only alter one triplet, and since the genetic code is degenerate, it may be that the new triplet encodes the same amino acid and that this mutation is silent and does not affect the individual. If the mutation creates a stop triplet it will generate a shorter protein. If it affects the stop codon, the synthesized protein will be longer, until another stop codon appears. If the mutation creates an amino acid other than the active center of the enzyme, the function of the protein will also be altered. If that protein improved the original, the individual would have an advantage over the rest of the population and could transmit it to their offspring.