Dictionary > Monozygotic twins

Monozygotic twins

monozygotic twins definition

Monozygotic twins
n., ˌmɒnəʊzaɪˈɡɒtɪk twɪns
Twins that developed from a single zygote

Monozygotic Twins Definition

Monozygotic twins are twins that developed from a single zygote. Etymologically, the term is derived from mono, meaning “one”, and zygotic, from zygote (from zugoun, meaning “to join”). The zygote splits into two equal halves, each independently growing into an individual with the same sex and genetic constitution as the other.

Abbreviation: MZ twins.
Synonyms: identical twins; enzygotic twins; true twins; uniovular twins; monovular twins; monochorial twins.
Compare: dizygotic twins.


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 that splits, forming two embryos. They are always of the same sex, i.e. both males or both females. (Ref. 1) They have the same genetic constitution. (Ref. 2) They have the same blood groups. They are physically alike or identical; thus, they are also called “identical twins”. (Ref. 1)

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. (Ref. 3)

See Also


  1. Identical Twins. (2020). Genome.Gov. https://www.genome.gov/genetics-glossary/identical-twins
  2. Insights From Identical Twins. (2013). Utah.Edu. https://learn.genetics.utah.edu/content/epigenetics/twins/
  3. 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.

Further reading

  • Do Identical Twins Have the Same DNA? – BioTechniques. (2018, November 26). BioTechniques. https://www.biotechniques.com/omics/not-so-identical-twins/ (Monozygotic twins can still be phenotypically different.)

©BiologyOnline. Content provided and moderated by BiologyOnline Editors.

You will also like...