Mutations and Their Effects — AQA GCSE Biology
Mutations are random changes to the DNA base sequence. They are the ultimate source of genetic variation.
What is a mutation?
A mutation is a random change to the DNA base sequence. Mutations occur continuously and their rate can be increased by factors such as radiation and some chemicals.
Effects of mutations
Most mutations have no effect on the protein produced. However:
- Some mutations alter the shape of a protein (for example, an enzyme's active site may change so the substrate no longer fits, or a structural protein may be weakened).
- A mutation in a non-coding region of DNA may affect how genes are switched on or off.
Very rarely, a mutation produces a new characteristic. If this gives a survival advantage in the organism's environment, it may become more common through natural selection — this is how evolution can occur.
Coding and non-coding DNA (Separate)
- Mutations in the coding DNA can change the amino acid sequence and the protein.
- Some non-coding DNA switches genes on and off; mutations here can affect how proteins are made.
Exam tips
- Define a mutation as a random change to the DNA base sequence.
- Most have no effect; some change a protein's shape/function.
- A beneficial mutation can spread by natural selection (link to evolution).
- Radiation and certain chemicals increase the mutation rate.