Discuss the maternal immune hypothesis

Question

What will be an ideal response?

Answer 1

Answer: The maternal immune hypothesis is one model of the cause of the fraternal birth order effect. In this theory, the H-Y androgens (male hormones regulated by a gene on the Y chromosome) are different enough from the mother’s antigens to trigger an allergic or immune system response. H-Y antigens are present in male but not female fetuses and do cross the placental barrier, which could trigger an immune response from the mother. The mother’s antibodies then react by attacking the H-Y antigen, preventing the fetal brain from developing male-typical brain structures and behaviors. Each subsequent male fetus increases the sensitivity of the mother’s immune system to the antigen. This is a common event in allergy development. This model has been tested experimentally and anti-H-Y antibodies in utero have been shown to disrupt later sexual behavior in male mice. In humans, evidence shows that H-Y antigens can cross the placental barrier, that the maternal immune response is greater to cells from males than females, and that newborn boys with older brothers tend to have a lower birth weight than boys with older sisters.