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
- chemical mutagen, such as tar from cigarette smoke
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.
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.
Inversion
In this image the order of the bases has changed. The second C and first A bases have swapped positions. As the bases are read in threes’ (triplet code) this may result in a different amino acid being synthesised, and therefore possibly a different protein eg CAC 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 cystic fibrosis.