In Judaism, a Jewish mother gives birth to a Jew. So in order for someone to be born Jewish, the mother has to be Jewish.
While innate "Jewishness" is given by the mother to her children (even if they are baptized Christian, they are still Jewish as far as the law is concerned), the blood line is inherited through the father.
This law goes back to the times when the Jews were polygamists. As long as the father was known, the family was intact regardless of who the mother was (the reverse, one woman having more than one husband, doesn't work, and the family unit falls apart).
I suspect that one of the reasons the Jews did not accept Jesus as the descendant of David is precisely because the man who they though was His father (+Joseph) did not have a clean bill of lineage in that respect, but somewhat remotely, not from the "choice stock" so to say. The Gentiles (primarily Greeks), on the other hand, for whom the Gospels were written after all, the Davidian lineage was much easier to accept.
I always found the attempt by the Apostles to link Christ to King David using Mary as less then convincing for the Jewish consumption.
But one must also be a little careful when we speak of DNA. Two strands of DNA are required for conception, one set from the father, the other form the mother. Each set (in the egg and sperm) are haploids (cells containing only half the DNA required; trouble is, Mary's egg would contain only the female half). Ooops, there goes the touched-her-egg theory!
The only way that Christ could have ended up with both sets of Mary's DNA signature is by using her existing flesh (or bone or hair, or any part of her body (a product of her mothers' and her father's DNA, and not her egg).
So the Gospels writers knew that it had to be a mysterious and miraculous, supernatural event in order for it to be true, even though they didn't know any of the modern microbiology!
Except that we are not just made up of "flesh." Christ would have had to use every part of Mary's anatomy (save for reporoductive organs) to fashion His own body of out it. Or, He would have had to turn the differentiated tissues into the premordial embryonic cells ("stem cells") that could then differentiate into a human being, but He would have had to change the chromosomal makeup of Mary's embryonic cells from XX to XY in order for His flesh to be that of a man.
No matter how you take it, not only the Mary's seedless "conception" (the appearance of God the Word in her womb), but the actual "pregnancy" (i.e. the Incarnated God the Word, embryonic Jesus if you will) are of profoundly miraculous character, unlike anything we have ever seen or known in all of human history.
Knowing all this, insisting on His birth bieng "natural" is just plain naïve, in sharp contract to His appearance and incarnation in Mary's body. It is not His brith that makes Him a human, but Mary's "flesh" as they say. So, having a "normal" birth, after having undergone a highly miraculous conception and pregnancy, lacks any logic or justification.
The apostles didn't at all link Christ to David through Mary -- they did it through his legal adoptive father, Joseph. Both genealogies go from David to Joseph. One involves an episode of a brother raising up seed, legally, for his brother. The other is a pure bloodline.
A normal birth is simply the culmination of the initial incarnation that was Mary becoming pregnant. There is no logical justification for a miraculous birth. In fact, it shows that the virgin pregnancy was not needed and simply an arbitrary happening.
How so? The Spirit added the equivalent of male human DNA to join with Mary's egg so that she "conceived". No sex was involved. How is this inconsistent with your set-up?
The only way that Christ could have ended up with both sets of Mary's DNA signature is by using her existing flesh (or bone or hair, or any part of her body (a product of her mothers' and her father's DNA, and not her egg).
I agree. I'm not saying that I think that Jesus was some kind of weird male clone of Mary. He wasn't. I think He was FULLY human which means having the "normal" DNA structure, which was supplied by both Mary and the Spirit. My opinion is that it was God's version of some sort of supernatural artificial insemination.
Knowing all this, insisting on His birth being "natural" is just plain naïve, in sharp contrast to His appearance and incarnation in Mary's body.
You appear to hold the view that "Jesus the fetus" (sounds like a name for a Dave Barry rock band :) just popped into Mary's womb independent of any biological interaction with any part of Mary at all. That could be correct. I don't think the scriptures are clear enough for me to declare my view as a fact. However, as I have elsewhere posted, I think there is some scripture that supports my scenario and does allow for the pregnancy and birth to have been "normal". Given the importance of literal blood lines to the Jews of the time, how do you deal with the lineage requirement?