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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 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.
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 ...
Human genetic variation is the genetic differences in and among populations. There may be multiple variants of any given gene in the human population ( alleles ), a situation called polymorphism . No two humans are genetically identical.
Bouchard has said that these two twins happened to be unusually alike, while most twins show more differences: [4] There probably are genetic influences on almost all facets of human behavior, but the emphasis on the idiosyncratic characteristics is misleading. On average, identical twins raised separately are about 50 percent similar – and ...
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 ...
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 ...
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 ...