Is Sickle Cell Anemia a Dominant or Recessive Trait?

Sickle cell anemia is a disorder where abnormal hemoglobin is made, changing the structure of red blood cells. Humans inherit one set of chromosomes from their father and another set from their mother. Dominant traits require that only one parent pass on the gene for the trait. Recessive traits require both parents to pass on the genes. Sickle cell anemia is a recessive trait. People with one sickle cell gene are said to be carriers.

Sickle Cell Anemia

Sickle cell anemia is a disease where abnormal hemoglobin is produced by the body. This abnormal hemoglobin changes the shape of red blood cells from the normal, round shape to an abnormal sickle (or "C") shape. Red blood cells with abnormal hemoglobin (called hemoglobin "S") cannot move around the veins and arteries as well as normal cells, leading to the complications seen in patients with sickle cell anemia. Sickle cell anemia is not life-threatening; people with it resist blood parasite infections like malaria.

Heredity

Human beings have 23 pairs of chromosomes, which are bundled packages of DNA. Each chromosome has different genes, or DNA codes, that guide the body in creating everything from hemoglobin to brown or blond hair. Humans get one set of 23 chromosomes from their father and another set of 23 from their mother. This is why humans are a blend of traits, like eye color or height, from their parents.

Dominant Traits

Each trait we inherit comes in genes, and these genes pair up in our chromosomes. Some traits are said to be dominant when only one gene is needed for that trait to be displayed. For example, brown eyes are dominant over blue eyes, so only one parent needs to pass on the brown-eyed gene for the child to have brown eyes, even if the other parent has blue eyes.

Recessive Traits

Recessive traits require both set of genes to be the same in order to be inherited. In the example above, blue eyes are recessive. As a result, both parents must pass on the blue-eyed gene for the child to have blue eyes. When it comes to sickle cell anemia, the gene that codes for hemoglobin S is recessive.

Sickle Cell Anemia Heredity

Heredity chart for sickle cell anemia from the National Heart Lung and Blood Institute

If only one parent has the sickle cell anemia gene, the child who inherits it is said to be a sickle cell carrier. Carriers live normal lives with no anemia. However, carriers might pass on the trait to their children. If both parents pass on the sickle cell anemia gene, then the child who inherits them will have sickle cell anemia.

References

• National Heart Lung and Blood Institute, "What is Sickle Cell Anemia"
• Medline, "Sickle Cell Anemia"
• Human Genome Project Online