Being a carrier of genes that cause a particular disease does not mean that one actually has the disease; it simply means that one can pass this disease on to one’s children. If one or both parents test positive for a particular disease, this means they have an increased chance of giving birth to a child born with this disease. It does not, however, guarantee with utmost certainty that the child will have the disease – if both parents are carriers of a disease, there is a 1-in-4 (25%) chance their child will be afflicted. If one parent is already afflicted with one of these diseases and the other parent is a carrier, there is a 1-in-2 (50%) chance the child will be afflicted.