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Mutations and their effects
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A mutation is a change in DNA. Most do nothing, but a few change a protein and so change the phenotype.
From DNA to phenotype
A mutation changes the sequence of bases in DNA.
This can change the sequence of amino acids in a protein.
The protein may fold into a different shape and stop working (for example, an enzyme's active site may change). This can change the phenotype.
This can change the sequence of amino acids in a protein.
The protein may fold into a different shape and stop working (for example, an enzyme's active site may change). This can change the phenotype.
Size of the effect
Most mutations have no effect on the phenotype, for example if the changed codon still codes for the same amino acid, or the change is in DNA that does not code for a protein.
Some have a small effect.
Rarely, a mutation has a significant effect, which may be harmful or, occasionally, useful.
Some have a small effect.
Rarely, a mutation has a significant effect, which may be harmful or, occasionally, useful.
Increasing the mutation rate
Mutations happen naturally at random, but the rate is increased by:
Ionising radiation: gamma rays, X-rays and ultraviolet rays.
Chemical mutagens: for example, chemicals in tobacco smoke.
Ionising radiation: gamma rays, X-rays and ultraviolet rays.
Chemical mutagens: for example, chemicals in tobacco smoke.
Explain how a single change in a gene could stop an enzyme working.
- The base sequence changes, so a codon may code for a different amino acid.
- The amino acid sequence changes, so the protein folds differently.
- The active site changes shape, so the substrate no longer fits.
Answer: Changed base sequence, changed amino acid sequence, changed active site shape.
A mutation changes the base sequence of DNA, which can change the amino acid sequence and shape of a protein, affecting the phenotype. Most mutations have no effect, some a small effect and rarely a significant one. Ionising radiation and chemical mutagens increase the mutation rate.
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