David — it is certainly true, as you write, that the result of conception is an embryo with “distinct DNA.”
What’s not clear to me, however, is why “distinct DNA” should be the criterion by which we judge personhood for moral and legal purposes. As Reason’s Ronald Bailey has pointed out, 60 to 80 percent of human embryos — post-conception, with distinct DNA — are naturally destroyed by the woman’s body. Are we to see this as a large-scale massacre of human beings, develop drugs to prevent it from happening, and require all women who have unprotected sex to take them? Certainly, we would be willing to take measures like this if post-birth infants were dying in comparable numbers.