Sickle Cell Anemia is also called a recessive disorder, because if you do not have two copies of sickle hemoglobin gene, you will not have the disorder.
In this case th carrier will have one normal hemoglobin gene, and the other will be a sickle hemoglobin gene, or "Hh" in the scheme. The parent that has the disease will be labeled "hh" because he does have two copies of the sickle hemoglobin gene. When these two parents have children, none of them will be unaffected - they will either be a carrier, or will be sick. The combinations are: Hh - carrier, hh - disease, Hh - carrier and hh - disease. So, there is 50% chance that the child will have the anemia, and 50% chance that the child will be a carrier.
