Genetics of Sickle Cell Anemia Modified from a lab written by Dr. Janet Lanza Biology Department, University of Arkansas at Little Rock What is Sickle Cell Anemia? Red blood cells with normal hemoglobin (HbA) move easily through the bloodstream, delivering oxygen to all of the cells of the body. Normal red blood cells are shaped like jelly-filled doughnuts with a depression in the center and they are soft and flexible. Sickle cell anemia occurs when an abnormal form of hemoglobin (HbS) is produced. HbS molecules tend to clump together, making red blood cells sticky, stiff, and more fragile. Red blood cells containing HbS can clog blood vessels, deprive the bodyâs tissues and organs of the oxygen they need, and are short-lived. Normal red blood cells last about 4 months in the bloodstream but sickle cells only last 10 to 20 days, which causes anemia (a low number of red blood cells). People who are anemic tire more easily and often feel weak (NIH, 2007). Sickle cell anemia is not contagious and cannot be passed from one person to another like a cold or other infection. People with sickle cell anemia have inherited two sickle cell alleles, one from each parent. A child who has inherited the sickle cell allele from only one parent will not develop the disease, but they do carry the sickle cell trait. People carrying a single sickle cell allele can pass the trait to their own children. One would think that there is little reason for sickle cell disease to remain in the any human population since natural selection should favor reduction of the frequency of the sickle cell allele to near zero. For example, individuals who carry two copies of the sickle cell allele typically die before reaching reproductive age, which will reduce the frequency of the allele in a population and minimize its transfer between generations.