DNA

Chromosomes are X-shaped objects found in the nucleus of most cells. They consist of long strands of a substance called deoxyribonucleic acid, or DNA for short. A section of DNA that has the genetic code for making a particular protein is called a gene.

The gene is the unit of inheritance, and each chromosome may have several thousand genes. We inherit particular chromosomes from our parents.  The genes on those chromosomes carry the code that determines our physical characteristics, which are a combination of those of our two parents.

Cystic fibrosis

People with cystic fibrosis have inherited two faulty alleles, one from their father and one from their mother. They produce unusually thick and sticky mucus in their lungs and airways. Their lungs become congested with mucus, and they are more likely to get respiratory infections. Daily physiotherapy helps to relieve congestion, whileantibiotics are used to fight infection. The disorder also affects the gut and pancreas, so that food is not digested efficiently.

Genetic disorders

A person with cystic fibrosis has inherited two faulty alleles for a certain gene on one of their chromosomes, chromosome 7. It is hoped that it may one day be possible to repair the faulty alleles using gene therapy, perhaps by putting the normal allele into the cells of the lungs. This would greatly improve the lives of people with cystic fibrosis, who often need lung transplants as their illness progresses.

Breast cancer

Members of some families are particularly at risk of developing certain types of breast cancer, because they carry faulty alleles. These alleles have been identified, and it is now possible to test people to see if they have an increased risk of developing breast cancer. This allows them to make decisions, if they wish, about whether to have surgery to remove breast tissue before any cancer develops in their breasts.

Each gene in a molecule of DNA contains:

• A different sequence of bases
• Codes for a particular protein

Proteins are made in the cytoplasm of a cell, not in the nucleus. Genes cannot leave the nucleus, so a copy of the gene is needed. This copy is able to leave the nucleus to go into the cytoplasm so that proteins can be made by the cell.

Each gene in a molecule of DNA contains:

• A different sequence of bases
• Codes for a particular protein

Proteins are made in the cytoplasm of a cell, not in the nucleus. Genes cannot leave the nucleus, so a copy of the gene is needed. This copy is able to leave the nucleus to go into the cytoplasm so that proteins can be made by the cell.