Oh my, it's been a while that I saw Dark Angel. Not sure how much I remember but I don't think that will be needed reading the story here. And maybe I remember more than I think now. (I liked it back then,)
Nice twist, added the vampire traits to the DNA. But Buffy was only a minute under the influence of Marcus' DNA.
Looking forward to what being half-vamp does mean for the kids.
(I noticed that you don't use text with automatic word wraparound / continuous text / justified alignment ? Not sure how it is called. I've noticed because I make the text bigger and can see where you used 'enter key'.)