2.10: Monozygotic and Dizygotic Twins
- Page ID
- 233820
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Fig. 2.10. Identical Twins : 1 egg and sperm; same placenta, separate amniotic sacs. Fraternal twins: 2 eggs and 3 sperms separate placentas and separate amniotic sacs.
Image Source: Aryal, Sagar. Twins- Types, Causes and Significance. Microbe Notes. August 2023.
Identical Twins
Mononozygotic twins (identical twins) occur when a fertilized egg splits apart in the first two weeks of development. The result is the creation of two separate, but genetically identical offspring. They possess the same genotype and often the same phenotype. About 1/3 of twins are monozygotic twins.
Image Source: Renee Mendonca77. Twins Renee and Rhea. Wikimedia Commons.
Fraternal Twins
Dizygotic twins (fraternal twins) occur when two eggs or ova are released and fertilized by two separate sperm. These two individuals share the same amount of genetic material as would any two non-twin children from the same mother and father. In other words, they possess a different genotype and phenotype.
- Older mothers are more likely to have dizygotic twins than are younger mothers, and couples who use fertility drugs are also more likely to give birth to dizygotic twins.
Image Source: Mheref36.Twin Brothers Alike. Wikimedia Commons. Image Source: Dpulitzer. Red Hair Twins. Wkikmedia Commons
Source
- Lally, Martha and Suzanne Valentine-French. Lifespan Development: A Psychological Perspective. Licensed under CC BY-NC-SA 3.0.