The answer to this question would be zygote as the is the first stage in the reproduction process. Then the zygote will go on to become an embryo which will then later develop into a fetus and finally a baby.
This cell, formed by the union of an ovum and a sperm (Gr. zyg tos, yoked together), represents the beginning of a human being. The common expression 'fertilized ovum' refers to the zygote."
