opposed to di-zygotic twins are always of the same sex because they develop from the same ovum, which simply splits in the early stages of mitosis (cell division) which forms two individuals which carry the exact same genetic data.

MONOZYGOTIC TWINS (MZ TWINS): "Monozygotic twins will develop and become genetically identical twins due to not splitting apart during the process of mitosis within the womb."
Cite this page: N., Pam M.S., "MONOZYGOTIC TWINS (MZ TWINS)," in, April 7, 2013, (accessed October 24, 2020).