Final answer:
The infant most likely to have Rh incompatibility is one whose mother is Rh-negative and whose homozygous Rh-positive father ensures the child will be Rh-positive, leading to potential sensitization of the mother and risk of hemolytic disease of the newborn in subsequent pregnancies.
Step-by-step explanation:
The infant more likely to have Rh incompatibility is a) Infant of an Rh-negative mother and a father who is Rh positive and homozygous for the Rh factor. Rh incompatibility occurs when an Rh-negative mother becomes sensitized to Rh-positive fetal blood cells, which can happen during pregnancy or at childbirth. The Rh-positive father who is homozygous for the Rh factor will always pass the Rh-positive gene to the child, leading to Rh incompatibility if the child is Rh-positive and the mother is Rh-negative.
Understanding that antibodies against the Rh factor are not preformed but rather produced after exposure to the antigen is crucial. The first exposure, which might occur during the birth of an Rh-positive baby, leads to a primary immune response but typically does not affect the first Rh-positive baby significantly since the mother takes time to mount this response. However, in subsequent pregnancies with an Rh-positive baby, the mother's immune system will already be primed, and the secondary response will produce more antibodies that can cross the placenta and lead to hemolytic disease of the newborn (HDN).