This article waslast modified on 10 July 2017.
Genes are instructions for our body.  Normally genes are inherited in pairs – one from each parent.  A dominant gene needs only one of the pair to cause a change.  A recessive gene will not act on the body unless both of the pair are the same.  For example, the gene for cystic fibrosis is recessive and will not cause disease if a normal gene (which is dominant) is present.  It is therefore only possible to develop cystic fibrosis if both parents pass on a cystic fibrosis gene.