There is, I think, a problem with the entire thrust of the OP; science can only concern itself with definitions and properties in a strictly factual manner; science may well define me as a human being but falls silent on whether I have any right to live or be free; this task must be performed by systems of ethics, inspired by religion or otherwise; once defined, we can apply the ethical framework with rigour and accuracy, but that doesn’t make the ethical framework a scientific one.
Similarly, the definition ‘human’ isn’t one that springs naturally out of simple observation; it is primarily based on ideas; your idea that ‘human’ means any individual organism that contains a full set of unique human chromosomes; somebody else’s definition that is based on the presence of a nervous and circulatory system; another person’s definition that requires the individual to be capable of independent survival (which we can further pick at and wonder about the independence of toddlers).
godogsgo13; you describe the (anticipated) comparison to skin cells as ridiculous and yet at the point of fertilisation, there’s just a single cell; OK it divides a few times and becomes a ball of cells, but we could just as easily argue that until it implants in the wall of the uterus, it has no survival prospects and is just a rather interesting ball of cells.
Let me pick a little further and ask; do you believe that every time an egg is fertilised and fails to implant (and I’m led to believe that this is very common), that this is the death of a human being occurring?