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.