Sickle-cell anemia is a disease of the red blood cells. A person who carries one sickle-cell gene is physically normal, but has the potential to pass on the sickle-cell trait to his or her offspring. In a person with two sickle-cell genes, the blood cells collapse and cannot carry enough oxygen to the body's cells. This person can have fatal anemia. Based on this information, which statement best describes the gene for sickle-cell anemia? A. It is an acquired gene. B. It is a sex-linked gene. C. It is a dominant gene. D. It is a recessive gene.

The sickle cell anemia trait is found on a recessive allele of the hemoglobin gene. This means that you must have two copies of the recessive allele — one from your mother and one from your father — to have the condition. People who have one dominant and one recessive copy of the allele won't have sickle cell anemia.

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