John and jane are planning a family, but each has a brother who has sickle-cell disease, so they are concerned that their children may develop sickle-cell disease. neither john, jane, nor their respective parents have the disease. they consult a genetic counselor who tells them that a) there is no chance that any of their children will have sickle-cell diseaseb) all of their children will have sickle-cell diseasec) one of four of their children can be expected to have sickle-cell diseased) it's possible that none of their children will have the disease, but blood tests on them both will be required to make sure