What's your blood type?
The Rh-negative individuals have 2 Rh-negative genes presented in their DNA, resulting in no Rh-antigens on the red blood cells. On the other hand, the Rh-positive gene is dominant over the negative one: if one or two Rh-positive genes are presented, that person will be Rh-positive. The persons with 1 Rh-positive gene & 1 negative gene are called carriers, for they can pass on the Rh-negative gene despite being Rh-positive. A carrier parent has a 50:50 chance of giving his or her child a Rh-positive or negative gene.
If both parents are such carriers, what is the chance that their child will be a carrier, too?