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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 ...
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.
[citation needed] Twins are siblings that are born from the same pregnancy. [6] Often, twins with a close relationship will develop a twin language from infanthood, a language only shared and understood between the two. Studies corroborate that identical twins appear to display more twin talk than fraternal twins. At about 3, twin talk usually ...
Identical twins of the ‘Ask Reddit’ community recently shared what are the main differences between them and their sibling, showing that the dissimilarities can range from a unique mole to one ...
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).
Dizygotic (fraternal) twins can be caused by a hyperovulation gene in the mother. [8] Although the father's genes do not influence the woman's chances of having twins, he could influence his children's chances of having twins by passing on a copy of the hyperovulation gene to them. Monozygotic (identical) twins do not run in families.
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.
The mean correlation of IQ scores between monozygotic twins was 0.86, between siblings 0.47, between half-siblings 0.31, and between cousins 0.15. [ 81 ] The 2006 edition of Assessing adolescent and adult intelligence by Alan S. Kaufman and Elizabeth O. Lichtenberger reports correlations of 0.86 for identical twins raised together compared to 0 ...