Mutations - Higher

A mutation is a change in a gene or chromosome. It is a rare, random change in the genetic material and it can be inherited.

Causes of mutation

Mutation occurs continuously and can be spontaneous. It can also happen because of:

Ionising radiation includes gamma rays, X-rays and ultraviolet rays. The greater the dose of radiation a cell gets, the greater the chance of a mutation.

The radiation warning sign. A black circle with three triangular blades on a yellow background.
The radiation warning sign

Mutations could cause different genes to be switched on or off, and this could create a different or faulty protein to be synthesised. For example, if the protein is an important enzyme, the specific substrate might not fit into the substrate binding site. If it is a structural protein such as collagen, it might lose its strength.

However, most DNA mutations do not significantly alter a protein, they only alter it slightly, or not at all, so its appearance or function is not changed.

Mutations can be positive and give an organism an advantage or negative and give a disadvantage but mutations that have a significant effect are rare. Some mutations may have a small effect but most mutations have no effect on the organism. They do not change to the organism's phenotype.

These mutations may change the activity of a protein if they occur within a gene. This might result in a change in phenotype or it might appear hidden, and be unnoticed. Alternatively, they might result in a serious consequence, such as genetic disease like as cystic fibrosis.

Diagram showing the normal gene structure in DNA

Original gene structure

There are many different types of mutations which can arise in DNA. This diagram shows the normal order of the bases for one of the strands in a DNA molecule. Only one of the strands of DNA is involved in protein synthesis. A change from the normal order of bases leads to different types of gene mutation eg CGA / ACC / CGA.

These mutations may change the activity of a protein if they occur within a gene. This might result in a change in phenotype or it might appear hidden, and be unnoticed. Alternatively, they might result in a serious consequence, such as genetic disease like as cystic fibrosis.