Overview

What are genes?

Genes are the part of a body cell that contain the biological information that parents pass to their children. Genes control the growth and development of cells. Genes are made of DNA (deoxyribonucleic acid), a substance inside the centre (nucleus) of cells that contains instructions for the development of the cell.

You inherit half of your genetic information from your mother and the other half from your father. Genes, alone or in combination, determine what features (genetic traits) a person inherits from his or her parents, such as blood type, hair colour, eye colour, and other characteristics, including risks of developing certain diseases. Certain changes in genes or chromosomes may cause problems in various body processes or functions.

What are chromosomes?

Many genes together make up larger structures within the cell called chromosomes. Each cell normally contains 23 pairs of chromosomes.

A human has 46 chromosomes (23 pairs). One chromosome from each pair comes from the mother, and one chromosome from each pair comes from the father. One of the 23 pairs determines your sex. These sex chromosomes are called X and Y.

• For a child to be female, she must inherit an X chromosome from each parent (XX).
• For a child to be male, he must inherit an X chromosome from his mother and a Y chromosome from his father (XY).

Some genetic conditions are caused when all or part of a chromosome is missing or when an extra chromosome or chromosome fragment is present.

What is genetic testing?

Genetic testing includes any type of test that checks a person's DNA. Tests often use a sample of cells or tissue to look for changes in genes, chromosomes, or proteins. These changes can be a sign of a disease or a sign of an increased risk for getting a disease.

Testing may be done to:

• Find out if you carry a gene for an inherited disease, such as cystic fibrosis.
• Find out if your fetus is at risk for a genetic condition such as Down syndrome.
• Find out if you carry a gene that increases your risk for a disease later in life, such as breast cancer.
• Find out if you have an inherited heart disease called hypertrophic cardiomyopathy.
• Check for genetic changes that may affect your treatment for an existing disease.
• Find out if you have inherited gene changes that affect your response to medicines.
• Identify family members, crime suspects, or victims of war or disasters for legal purposes.

How can genetic counselling help?

The results of genetic testing can affect your life. It may be a good idea to get genetic counselling before deciding to have testing. Genetic counsellors can explain the pros and cons of testing, but you make the decision about whether to have the test. A genetic counsellor can help you make well-informed decisions. Genetic counselling can help you and your family:

• Understand medical facts about a disease and what you may be able to do to manage it.
• Understand how your family history contributes to the development of a disease.
• Explain the results of a genetic test.
• Help you find resources, including getting referrals to specialists or finding local support groups.

Genetic counsellors have specialized training in medical genetics and counselling. They are sensitive to the physical and emotional aspects of these decisions. Your privacy and confidentiality are carefully protected.