Which type of mutation results in the replacement of one nucleotide by another

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There are lots of different mutations that can occur in our DNA.

Small-scale mutations

• Point mutation – a change in one base in the DNA sequence.

• Substitution – when one or more bases in the sequence is replaced by the same number of bases (for example, a cytosine substituted for an adenine).

• Inversion – when a segment of a chromosome is reversed end to end.

• Insertion – when a base is added to the sequence.

• Deletion – when a base is deleted from the sequence.

Large-scale mutations

• Copy number variation (CNV) is a type of mutation where large chunks of DNA are inserted, repeated or lost. These regions of DNA can be between 10,000 and 5,000,000 bases long.
• Duplication of genes. When there is an increase in the number of copies of a gene.
• Deletions of large regions of the chromosome.
• Loss of one copy of a gene in an organism that previously had two copies.
• Loss of both copies of the same gene.
• Movement of sections of DNA from one location to another.
• Addition of an extra copy of a chromosome. For example, an extra copy/partial copy of chromosome 21 results in Down’s syndrome.

How do we inherit mutations?

• Each of our genes is a copy from either our mum or our dad. If there is a mutation in one of these genes, this can be passed on from parent to child along with the rest of their genes.
• Small inherited changes can make big differences to our bodies. For example, the most common mutation to cause cystic fibrosis is the loss of three letters in a gene called CFTR.
• Even though mutation is common, inherited diseases are relatively rare. This is because inherited diseases are often recessive, which means that a person must have two copies of the mutated gene to get the disease.

Image credits: Genome Research Limited

This page was last updated on 2021-07-21

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