Genes are sections of the DNA. Each gene has the code for creating a specific protein. Chromosome 27 is where the CFTR gene is located.

The sequence of bases in the gene controls which amino acids are created and joined to make a specific new protein (or enzyme) molecule. The primary structure determines structure and properties of the protein – getting the wrong amino acid in the sequence alters the shape because the protein won’t fold properly and thus won’t be able to function.

Each DNA strand is made up of thousands of different genes, combining those hundreds of thousands of different genes, in different patterns and combinations, would make a really huge number of unique individuals, hence we all look physically different (except identical twins).


Genome = all the genes in an individual


Mutations are changes that can occur in genes. These changes are random and can be caused by background radiation and chemicals that we come into contact with, e.g. the chemicals in cigarette smoke. The change causes an alteration to the base pair sequence in the genetic code.

Sometimes these changes can be so severe that the cell dies, sometimes the cell can divide uncontrollably and become cancerous, and sometimes the changes are small and the cell survives. Very rarely, the changes may even be beneficial to us and produce new and useful characteristics.


Passing on mutations

If these changes occur in normal body cells, the changes are lost when we die. But if the changes occur in our sex cells such as sperm and ova, there is the possibility that the changes in the gene will be passed onto the next generation.

Types of mutations


  • Mutations that are passed from parent to child are called hereditary mutations or germline mutations (because they are present in the egg and sperm cells, which are also called germ cells). This type of mutation is present throughout a person’s life in virtually every cell in the body.


  • Acquired (or somatic) mutations occur in the DNA of individual cells at some time during a person’s life. These changes can be caused by environmental factors such as ultraviolet radiation from the sun, or can occur if a mistake is made as DNA copies itself during cell division. Acquired mutations in somatic cells (cells other than sperm and egg cells) cannot be passed on to the next generation.


  • Mutations may also occur in a single cell within an early embryo. As all the cells divide during growth and development, the individual will have some cells with the mutation and some cells without the genetic change. This situation is called