A reference to an organism which develops from a zygote or a single cell (fertilized ovum): Dr. Smith told Melanie, that after the zygotic stage of development took place, she should really know if she was really pregnant after a few weeks at the latest.

A gene which allows the normal functioning of gametes (reproductive cells in animals and plants), but has deadly effects during embryonic or larval development: A zygotic lethal gene is a changed or an altered version of a healthy gene, which is necessary for viability of a zygote, and causes a deletion or loss of the entire gene.