A multiple birth occurs where more than one fetus exits the womb in a single pregnancy. Different names for multiple birth are used, depending on the actual multiple. Common multiples are two and three, known as twins and triplets respectively. Twins, triplets and other multiple births occur to varying degrees in most animal species, although the term is most applicable to species in placental species.
There are two types of multiple births, fraternal (dizygotic) and identical (monozygotic). Identical siblings arise where one egg is fertilised and the resulting zygote splits into more than one embryo. Identical siblings therefore have the same genetic material. Fraternal siblings result from the fertilisation and implantation of more than one egg, so fraternal siblings are not genetically identical.
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TwinStuff.com - Bulletin boards, twin games, photo gallery, information for parents, TV and movie twins, twin events, and information.
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Twinsworld - Offerings include a twin casting agency, twin events, reunion of twins placed for adoption or separated at birth, message boards, links, photos, contests, and research.
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The International Twins Association - A non-profit, family-oriented organization to promote the spiritual, intellectual, and social welfare of twins and multiples throughout the world.
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TwinMajority.org - From 2127, most babies will be twins. This site explains why evolution predicts this.
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Twins by Twins - This site is built for all those that want to learn more about twins and is dedicated to those that are twins and proud of it.
Twins Network - A resource for understanding twins and sharing information. Surveys, facts, news, trivia, links.
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TwinsRealm.com - Mirror twins from Australia share photos, twin stories, links and information on twin festivals and celebrations.
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