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Monozygotic twins

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Twins developed from a single zygote that split into two equal halves, each independently growing into an individual but having the same sex and genetic constitution as the other


Twins refer to the two offspring that are brought forth by the same pregnancy and birth. Twins may be monozygotic (or identical) or dizygotic (fraternal). Monozygotic twins are twins that develop from one zygote and splits, forming two embryos. They are always of the same sex, i.e. both males or both females. They have the same genetic constitution. They have the same blood groups. They are physically alike. They would also exhibit identical psychological and mental characteristics. Thus, they are also called identical twins.

Monozygotic twinning is assumed to form following the collapse of a blastocyst, resulting in the splitting of the progenitor cells in half. It occurs spontaneously or naturally. However, with the current technology, it can already be induced artificially through embryo splitting.1

Word origin: mono- (one) + zygotic (zygote) twins

Abbreviation / Acronym: MZ twins


  • enzygotic twins
  • identical twins
  • true twins
  • uniovular twins
  • monovular twins
  • monochorial twins


See also:

1 Illmensee, K., Levanduski, M., Vidali, A., Husami, N., and Goudas, V. T. (February 2009). "Human embryo twinning with applications in reproductive medicine". Fertil. Steril. 93 (2): 423–7.