{{Details|Twin|the terms "monozygotic" and "dizygotic"}}
As discussed above, "zygosity" can be used in the context of a specific genetic locus (example<ref>{{citePujol, C.; Messer, S.; Pfaller, M.; Soll, D. (2003). "Drug resistance is not directly affected by mating type locus zygosity in Candida albicans". Antimicrobial agents and chemotherapy 47 (4): 1207–1212. DOI:10.1128/AAC.47.4.1207-1212.2003. PMC 152535. PMID pmid|12654648}}. [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=152535].</ref>). In addition, the word "zygosity" may also be used to describe the genetic similarity or dissimilarity of twins.<ref>[http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=hmg Human Molecular Genetics], 2nd edition by Tom Strachan and Andrew P. Read [http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=hmg&part=A2178#A2306 Chapter 17]. (1999).</ref> Identical twins are '''monozygotic''', meaning that they develop from one zygote that splits and forms two embryos. Fraternal twins are '''dizygotic''' because they develop from two separate eggs that are fertilized by two separate [[sperm]].
