Mutation is an unpredictable change in the genetic material of an organism.

Mutations may also cause changes in the structure or number of whole chromosomes in a cell, in which case they are known as chromosome mutations (or chromosome aberrations).

A change in the structure of a DNA molecule, producing a different allele of a gene, is a gene mutation.

Causes of mutation

All types of ionising radiation (alpha, beta and gamma radiation) can damage DNA molecules, altering the structure of the bases within them.

Ultraviolet radiation has a similar effect, as do many chemicals – for example, mustard gas.

key words

A mutagen : a substance that increases the chances of mutation occurring.

Carcinogens: are cancer-causing compounds(e.g. UV light, Asbestos, Tar:Tar is a mixture of compounds that settles on the lining of the airways in the lungs and stimulates a series of changes that may lead to obstructive lung diseases and lung cancer ). These cause mutations in the genes that control cell division.

When control of the cell cycle has been lost a cell undergoes repeated uncontrolled divisions that produce a mass of cells called a primary tumour.

Primary tumours are often benign because they do not grow rapidly and do not spread, but others are malignant because cells become detached from them, are carried elsewhere in the body and there develop into a secondary tumour.

The spreading of cells to form tumours in a diferent part of the body is known as metastasis. Patients with secondary tumours are said to have cancer and unless the tumours are successully treated they are likely to lead to a patients death.

The steps involved in the development of cancer are shown