A dog is dog from the moment of conception. No doubt about it. He has dog DNA. If everything goes well, he will develop into a living, breathing dog. The same is true for a Homo Sapian. It is pure and simple (?) biology.
The question is what makes a human different than a dog. It is not just a set of dog or homo sapian DNA sequences. It is somthing else. Something that we all know is there but we can not lay our finger on precisely. For want of a better concept, most people call it a soul.
The soul is what makes man different than a another sequence of DNA. The soul is what makes a Homo Sapian a Human.
The question then becomes at what point does the soul merge with the Homo Sapian to make a Human.