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The human twin birth rate in the United States rose 76% from 1980 through 2009, from 9.4 to 16.7 twin sets (18.8 to 33.3 twins) per 1,000 births. [5] The Yoruba people have the highest rate of twinning in the world, at 45–50 twin sets (90–100 twins) per 1,000 live births, [6] [7] [8] possibly because of high consumption of a specific type of yam containing a natural phytoestrogen which may ...
The presence of a "T-sign" at the inter-twin membrane-placental junction is indicative of monochorionic-diamniotic twins (that is, the junction between the inter-twin membrane and the external rim forms a right angle), whereas dichorionic twins present with a "lambda (λ) sign" (that is, the chorion forms a wedge-shaped protrusion into the ...
Monoamniotic twins are identical or semi-identical twins that share the same amniotic sac within their mother's uterus. [1] Monoamniotic twins are always monochorionic and are usually termed Monoamniotic-Monochorionic ("MoMo" or "Mono Mono") twins. [1] [2] They share the placenta, but have two separate umbilical cords.
The power of twin designs arises from the fact that twins may be either identical (monozygotic (MZ), i.e. developing from a single fertilized egg and therefore sharing all of their polymorphic alleles) or fraternal (dizygotic (DZ), i.e. developing from two fertilized eggs and therefore sharing on average 50% of their alleles, the same level of genetic similarity found in non-twin siblings).
Neonatal mortality rate: Number of child deaths within the first 28 days of life divided by total number of births. [9] Infant mortality rate: Number of child deaths within the first 12 months of life divided by total number of births. [9] Under 5 mortality rates: Number of child deaths within the 5th birthday divided by total number of births. [9]
In 1982, twins who were born with two different skin colors were discovered to be conceived as a result of heteropaternal superfecundation. [7] [5] In 1995, a young woman gave birth to diamniotic monochorionic twins, who were originally assumed to be monozygotic twins until a paternity suit led to a DNA test. This led to the discovery that the ...
One of the twins (Polydeuces, Heracles) is the illegitimate son of the god Zeus; his brother is the son of their mother's mortal husband. A similar pair of twin sisters are Helen (of Troy) and Clytemnestra (who are also sisters of Castor and Polydeuces). The theme occurs in other mythologies as well, and is called superfecundation.
A second and more common design is the twin study in which the similarity of identical and fraternal twins is used to estimate heritability. These studies can be limited by the fact that identical twins are not completely genetically identical, potentially resulting in an underestimation of heritability.