Geeky Catholic Questions: Jesus's Y Chromosome

Every once in a while, I'll hear something in a homily or on Catholic radio that sparks a question. As I'm not an authority on Catholic theology, but I'd like to explore these topics a bit, so I've created the series "Geeky Catholic Questions." Today's question: Where did Jesus get his Y chromosome?

The Context
As Catholics, we believe that Mary is a very important figure in the Church. One of the reasons for her importance (of which there are too many to go into here) is that she provided Jesus's human nature. Jesus, as we know, is the Son of God, the Second Person of the Holy Trinity. He has two natures: human and divine. He has a divine nature by virtue of being God. But he also has a human nature.

While it is not necessary (or even possible) to scientifically explain every part of our faith, reason and faith work in harmony, and the former can often help enrich the latter. For example, God chose to redeem us by sending his only Son to become man and shed his blood for us. Jesus came into the world through Mary, and in fact received his blood from her. By understanding that, we can see Mary's role as intercessor.

So the other day, I was considering the scientific details of the incarnation, and got to thinking about genetics. Joseph was not the biological father of Jesus, so Jesus received all of his genetic material from Mary, right? All 23 pairs of chromosomes. But one of these pairs of chromosomes determines a person's sex. A female has two X chromosomes. A male has an X and a Y. Ordinarily, when conceiving a child, each parent provides half of each chromosome pair. The mother will provide an X chromosome, and the father either provides an X or a Y. [Incidentally, this is why it was actually Henry VIII's fault - and not the fault of any of his series of wives - that he did not conceive a son.] But Jesus's conception was not ordinary. As a man, he would have to have an X and a Y chromosome. So where did he get the Y?

The Answer(?)
The short answer to this question is that all things are possible for God. So this doesn't provide any kind of obstacle to my faith. The question is not whether Christ's conception was possible without a human father, but rather how God chose to bring it about.

Could God have used Joseph's DNA and miraculously inserted it into Mary to conceive Jesus, while preserving Mary's virginity? I guess, but that just seems unlikely that God would do that.

One possibility is that God created 23 chromosomes to pair with 23 of Mary's, thus providing the Y chromosome for Jesus. The other possibility is that God used 22 chromosome pairs and one X chromosome from Mary, and created one Y chromosome.

I like either one of these possibilities. In possessing Mary's DNA, Jesus inherits our humanity. Whereas if God had just created 23 brand new chromosome pairs and implanted them in Mary, Jesus would seem to be wholly disconnected from the rest of us. Not that his directly created genetic material would make him non-human, but he would have a different lineage. But by God creating either a new Y chromosome or 23 new chromosomes, Jesus does become a "new Adam," who is not a fallen creature. It also says something about Jesus's masculinity. He is the ultimate model of manhood. A man who does not use his strength to dominate others, but lays down his life for others. The source of this masculinity is not from fallen humanity, but from God.

As a disclaimer, all of this is mere speculation, and the Church has not ruled on this definitively. What we must believe is that Jesus is fully human and fully divine. Jesus became a mediator between humanity and God, so that we could be reconciled to Him.

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  1. Good point on Mother Mary being co-redimer if taking this way.


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