RH-negative blood parents may both be RH-negative, both may be RH-positive, or one may be negative and one positive. The gene for RH-negative blood is recessive, and if both parents are RH-negative, the children are usually RH-negative. If both parents are RH-positive, but both are carriers of the RH-negative gene, there is a 1 in 4 chance that the child will be RH-negative. If one parent is RH-negative and the other is a carrier of the RH-positive negative gene, the child has a 1/2 chance of being negative; if the other parent is RH-positive and does not carry the negative gene, the child is RH-positive. If the mother is RH-negative, special care should be taken during pregnancy, as blood group incompatibility may occur, which in severe cases can result in hemolytic jaundice. If there is a genetic variation, the blood group may appear to be inconsistent with the pattern of inheritance, and DNA analysis testing may be performed.