Final answer:
The recessive (d) allele in the Rh blood group system leads to Rh-negative individuals lacking the D antigen. During subsequent Rh-positive pregnancies, Rh-negative individuals can develop antibodies against Rh-positive cells, potentially resulting in hemolytic disease of the newborn if not treated with RhoGAM.
Step-by-step explanation:
The Rh antigen with the recessive (d) allele is significant in relation to blood types and transfusion compatibility. People who lack the D antigen, which is most significant among Rh antigens, are called Rh-negative (Rh-). The Rh D antigen plays an important role in transporting ions across cell membranes as it functions as a channel protein.
Individuals who are Rh-negative do not have this antigen on their erythrocytes, while those who are Rh-positive (Rh+) do. If an Rh-negative individual has a child who is Rh-positive, their body may produce antibodies against the D antigen. This is not problematic during the first pregnancy but can cause serious issues, such as hemolytic disease of the newborn, during subsequent Rh-positive pregnancies if not preventively treated with RhoGAM.
The hemolytic disease can occur because, during the birth of the first Rh-positive child, the Rh-negative parent may be exposed to Rh-positive fetal blood cells, leading to the production of primary anti-Rh antibodies. A subsequent Rh-positive pregnancy can then trigger these antibodies to cross the placenta and attack the fetus's Rh-positive blood cells, leading to anaemia and other health issues for the newborn.