Zona pellucida
A
glycoprotein coating that
surrounds the outer layer of the ovum (egg) and early embryo. The zona
pellucida disappears just prior to implantation of the early embryo into the
uterine wall.
Zygote ( fertilized egg )
The cell that results from fusion of a sperm and egg at
fertilization. After three divisions the zygote is called a morula.
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