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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 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 relative influence of genetics and environment for a trait can be calculated by measuring how strongly traits covary in people of a given genetic (unrelated, siblings, fraternal twins, or identical twins) and environmental (reared in the same family or not) relationship.
Sophie and Adrian are cousins, but also genetic siblings known as quaternary twins. Quaternary twins occur when one set of identical twins has children with another set of identical twins ...
But the most universally understood factor is the impact that genetics have. As an example, Clemente notes that dyslexia occurs in up to 68% of identical twins of individuals with dyslexia and up ...
Twin studies provide a unique opportunity to explore the genetic and environmental influences on autism spectrum disorder (ASD). By studying identical twins, who share identical DNA, and fraternal twins, who share about half of their DNA, researchers can estimate the heritability of autism by comparing the rates of when one twin is diagnosed with autism while the other is not in identical vs ...
For example, research has found that identical twins, who share 100 percent of their genetic material, almost always have matching hair whorls. However, a small percentage of identical twins show ...
The sex is not involved in heritability of personality traits, on the other end environmental differences can increase or decrease the importance of genetic factors. Twins data shows that genetic influences contribute to personality stability and are relatively constant with age whereas environmental influence on personality increases with age.