Why is Major Nikon asking this question of DUpipo, who for the most part hate and are ignorant of what Pro-Life people believe?
An egg or a sperm do not have a complete set of human chromosomes. They are merely cells in the female's or male's body and absent being part of fertilization will never become more. Once fertilization has taken place there is a genetically unique individual, no longer simply a cell of the woman's body. At that point the cell is alive and programmed to develop into a unique human body. So at the point of fertilization a unique human life has come into being. By the time the woman is sure she has missed her period, that new human being is 3 or 4 weeks into that development process. IOW, trying to nitpick the exact moment in the process of fertilization the human being came into being is academic ink-squirting; that moment passed weeks before the woman starts to wonder if she's pregnant.