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Chromosomes carry genetic information in a molecule called DNA. They are found in pairs in the nucleus of the cell, and consist of a linear arrangement of genes. Genes also exist in pairs, and each gene creates a code that makes a specific protein.

Mitosis is a type of cell division which ensures that, when a cell divides, each new cell produced has the same genetic information.

Each human body cell contains 46 chromosomes. These can be arranged into 23 pairs. Each chromosome in a pair carries the same types of genes.

Cell division

Cells divide when:

• an organism grows
• organisms need to replace worn-out cells
• organisms need to repair damaged tissue

During these processes, the cell undergoes a type of cell division called mitosis.

In mitosis, two cells called daughter cells are produced. It is essential that any new daughter cells produced contain genetic information that is identical to the mother cell, and that the number of chromosomes remains constant.

Cancer

Cells grow then divide by mitosis only when we need new ones – either when we’re growing, or need to replace old or damaged cells.

When a cell becomes cancerous, it begins to grow and divide uncontrollably. New cells are produced even if the body does not need them.

A group of cancerous cells produces a growth called a tumour.

What causes cancer?

Chemicals and other agents that can cause cancer are called carcinogens. Carcinogens cause cancer by damaging DNA which can cause mutations to occur. A single mutation will not cause cancer – several are required. For this reason, we are more likely to develop cancer as we get older.

There are certain genetic factors that increase the likelihood of developing some cancers. Something that increases the likelihood of developing a disease is called a risk factor. There are several risk factors for various types of cancers.

Lifestyle factors

• Viruses linked with cancer, such as the human papilloma virus (HPV), being spread from person to person through sexual intercourse.
• The chemical carcinogens in cigarette smoke increasing the risk of lung cancer.
• Alcohol intake is linked with certain cancers.
• Exposure to ultraviolet radiation, part of which is ionising, during sunbathing or outdoor activities, leading to the development of skin cancers.
• A poor diet with increased fat and salt intake, as well as the consumption of certain foods, can increase the risk of cancer.

Industrial and environmental factors

• Exposure to ionising radiation, like ultraviolet radiation in sunlight, increases the risk factor.
• Exposure to chemical carcinogens such as those in cigarette smoke.