DNA is the complex chemical that carries genetic information. DNA is contained in chromosomes, which are found in the nucleus of most cells. The gene is the unit of inheritance and different forms of the same gene are called alleles.

Cystic fibrosis is an inherited disorder caused by a faulty allele.

The Human Genome Project has worked out the human DNA sequence, and its data are useful for forensic science and medical research.

What is DNA?

You will remember from your Key Stage 3 studies that the cell's nucleus controls the activities of the cell. Look there if you need to remind yourself of animal and plant cells.

Chromosomes

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 through the egg of our mother and sperm of our father. The genes on…