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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).
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 ...
Monozygotic twins result from the fertilization of one egg and the division of that single embryo forming two embryos. [4] However, just because a set of twins share the same genetic information, it does not mean they will exhibit the same traits and behaviors. There are different versions of a gene, which are called alleles. How a gene is ...
Homopaternal superfecundation is fertilization of two separate ova from the same father, leading to fraternal twins, [3] while heteropaternal superfecundation is a form of atypical twinning where, genetically, the twins are half siblings – sharing the same mother, but with different fathers.
Twin studies are one method of testing genetic and environmental influences, although they cannot reveal what kind of environmental influence this may include (social or non-social). [29] Identical or monozygotic twins share their genes, while fraternal or dizygotic twins are only as genetically similar as any other sibling pair.
A U.K. woman who was told she would never have children because of a rare condition recently gave birth to twins. When Hayley Haynes was 19, she went to the doctor because she hadn't gotten her ...
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.
Conjoined twins, popularly referred to as Siamese twins, [1] [2] are twins joined in utero. [ a ] It is a very rare phenomenon, estimated to occur in anywhere between one in 50,000 births to one in 200,000 births, with a somewhat higher incidence in southwest Asia and Africa. [ 5 ]