A baby typically gets one gene from dad, one gene from mom. If both genes the baby gets are sickle cell gene, then the baby is going to have sickle cell disease. If the baby gets one sickle gene and one normal gene, the baby is called sickle cell trait, meaning he isn't gonna have sickle cell disease he carries the gene and may pass it to the next generation. Sickle cell disease occurs at a high percentage with African American, 1 out of 13 is carrying one sickle cell gene(sickle cell trait), the chance is much lower in other ethics, in Hispanic American it's 1/50 of African American. If both dad and mom have sickle cell disease, the baby gets sickle cell disease 100%. If both dad and mom carries one sickle gene (both are SCT), then 25% sickle cell disease, 50% SCT, 25% non SCT non disease. If one of the parents carries SCT, the other doesn't carry SCT, the baby has 50% chance of SCT, 50% chance of non SCT, 0% chance of sickle cell disease. I hope this can explain a bit.