Mutations

A mutation is a random change to genetic material. In the mutation shown below, a section of DNA, three base pairs long, has been lost.

DNA mutation. 2 DNA sequences.  The second is missing 3 pairs: TA, GC and CG.

DNA contains genes that carry instructions for the manufacture of a protein. If a mutation occurs in a gene that results in a change to the sequence of DNA bases, then the structure of the protein that is made may also be altered. This could alter an individual's phenotype.

A mutation can be neutral and have no effect or can have an advantageous or disadvantageous effect on an individual that possesses it. Mutations are the only source of new alleles.

MutationEffect on individual's ability to survive and reproduce
AdvantageousIncreased
DisadvantageousDecreased
NeutralNo change

Some people carry a mutated version of the gene that codes for haemoglobin. The protein that is coded for by the mutant allele doesn’t function correctly and can distort the shape of red blood cells.

Three circular red blood cellsThree circular red blood cells

If a person has two copies of the mutant allele in their body cells then they will have the genetic condition sickle cell anaemia. The sickle shaped red blood cells can block blood vessels and have a much shorter life span than normal red blood cells.

Mutations happen spontaneously. The rate of mutation can be increased by environmental factors such as UV radiation, X-rays, gamma rays and certain types of chemicals such as bromine.

A red blood cell with a distorted 'sickle' shapeA red blood cell with a distorted 'sickle' shape