I have never heard of this account before. I have always thought that the Spirit "produced" the necessary genetic material and caused it to unite with Mary's egg, (without any "union" in the human sense, of course). But you're saying that God just "zapped" a fertilized embryo into Mary's womb? So, Jesus did not have Mary's blood type or any of her DNA, that kind of thing? If true, that would definitely seem to throw new light onto the "birth-giver of God" vs. "Mother of God" debate.
For obvious reasons, none of the traditions of the Church deal with the genetics or embryology of what happened at the time of the Annunciation.
The terminology of the Church has been to say that he took flesh from the Virgin. His flesh was not created "de novo" and inserted into her womb, and she wasn't just some kind of "surrogate mother." She was Christ's mother in the flesh.
As to how this exactly took place from the point of view of modern biology, it is probably best not to pry and speculate, just as we Orthodox do not speculate on what happens with the bread and wine at the Divine Liturgy. We know that it is bread and wine, and that by the time we receive it, it is *also* the Body and Blood of Christ -- how this can be is a Mystery beyond our comprehension, thus our usual terminology is to say that we "receive the Holy Mysteries" when we commune.
We do not feel the need to explain everything, nor do we think that we have permission from God to explore beyond the bounds of what he has revealed to us.
Yep, I guess birth-giver is out and mother is back in. ,p.{^_^}