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Article: Twins
- Article from:
- Gale Encyclopedia of Children's Health: Infancy throughAdolescence
- Author:
CopyrightCOPYRIGHT 2006 Thomson Gale. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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Twins
Definition
Twins occur when two babies are born at the same birth.
Description
Identical, or monozygotic, twins are of the same sex and are genetically identical and physically similar, because they both come from one ovum (egg), which, after fertilization, divides in two and develops into two separate fetuses. Fraternal, or dizygotic, twins occur when the mother produces two eggs in one monthly cycle and both eggs are fertilized. The conceptions may take place on two separate occasions and could involve different fathers.
Fertilized egg division which produces twins can either happen early or late in development. In the case of early separation, the two fetuses either share ...