The chorionic membrane of the zygote has genes from the father and is therefore foreign to the mother's immune system.

Question

Quizplus · Accepted Answer

The chorionic membrane of the zygote is formed from cells of the fertilized ovum, which contain genes from both the mother and father. However, some of the paternal genes are expressed in the chorionic tissue, which makes it foreign to the mother's immune system. This is thought to be one of the reasons why the mother's immune system does not attack the developing fetus, despite the fact that it contains genes from both parents.

The Chorionic Membrane of the Zygote Has Genes from the Father