We agree that a zygote is alive. So the question is, is it a human person? And you answer depends upon how you define "human person". If you define it by DNA, then your answer will be yes. If you define it by brainwave activity, then your answer will be no. You cannot avoid the necessity of defining your terms.
But how do you define a "living human being"? Your definition is so broad ...The second sentence exposes the sophistry of asking for further definition by tacitly assuming that the phrase 'living human being' is, in fact self-defining!