A dominant gene is one that almost always results in a specific physical characteristic, for example, a disease, even though the patient's genome possesses only one copy. With a dominant gene, the chance of passing on the gene (and therefore the disease) to children is 50-50 in each pregnancy.
'Recessive' is a term used in genetics to describe one of the ways by which a gene is passed from parent to offspring. Many characteristics are determined by a single pair of genes, one of each pair , an allele being inherited from each parent. A recessive gene is overridden by an equivalent dominant gene.
For example, the gene for blue eye color is recessive; therefore, if a child inherits the gene for brown eyes from one parent and the gene for blues eyes from the other, the "blue eye" gene is overridden by the "brown eye" gene, and the child ends up with brown eyes. The child must inherit the recessive blue eye gene from both parents in order to develop blue eyes.
Recessive alleles were discovered by Gregor Mendel, who found that a cross between pure bred red- and white-flowering garden peas always produced red flowers in the offspring. The allele for red coloration is dominant; the allele for white is recessive.
Many genetic disorders are determined by a recessive gene. Examples include cystic fibrosis and sickle cell anemia. The child will only have the disease if he or she inherits the gene from both parents.