Cells of umbilical cord - mom's or son's?

Question

Let's say we have a mother giving a birth to a son. In a very clear manner the cells of these two individuals are very different, of course. Yet there is an umbilical cord connecting them. Then there should be a clearly defined "border" somewhere on its way where the mother's cells meet the cells of her son, is that so? How is it even possible?! ;)\n

Answer 1

The umbilical cord is part of the fetus in structure and genetics.