OK, padna, I'll try one more time.
Merely having human DNA is simply not enough to qualify in my opinion as an organism that deserves moral consideration for a couple of reasons. Morals are, from one perspective, a transaction between equals (simplified into the Golden Rule). This is what I'm talking about when I talk about 'moral agents'. A fetus, obviously, can't participate in that transaction. They aren't "an end unto themselves", to borrow Kant's phrase - in fact, biologically, a zygote, fetus, etc. actually is a means to an end (a fully formed human being).
Because that end is a human being though, there probably "ought" to be some special case here, just as there are special cases for children or adults with impaired brain functions. But that's where the utilitarian, 'maximal pleasure/minimal pain' argument comes in, and why I think the development of the fetal nervous system is relevant to the discussion. 'Minimal suffering' when aborting a first or early second trimester fetus can only refer to the health, physical or emotional, of the mother (and, if you want to include him in the discussion, the father) - and that's not a call I'd ever be willing to make for her. That necessarily can only be a highly personal decision on her part - and thus, as long as the fetus is not yet developed enough to feel pain from the abortion, I have to be pro-choice.
The other reason I think it's abhorrent to base moral decisions on the possession of human DNA is that you are a priori excluding every other sentient being, or even possibly sentient being, from consideration. Dolphins may very well be moral agents in their own right - they've shown the capacity for using tools and for inter-species empathy, and other behavior that at one time we would've considered exclusively human.
Your definition of who is "human" is based on the possession of human DNA, which is fine as far as it goes. But we're not talking about biology, we're talking about the morality of a specific action. And I'm just not comfortable basing a decision on who gets to be considered part of the most privileged class - who gets to be considered a "who" - based on that. It just doesn't seem relevant to me.
This is why a discussion of the building blocks of morality, and (for instance) why murder is wrong, is important. You can talk about it being self-evident and based on natural law all you want, but clearly abortion is not self-evidently right or wrong or the argument wouldn't have raged as long as it has. To me, that's just dodging the real heart of the question.