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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).
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.
The word zygosity may also be used to describe the genetic similarity or dissimilarity of twins. [6] Identical twins are monozygotic, meaning that they develop from one zygote that splits and forms two embryos. Fraternal twins are dizygotic because they develop from two separate oocytes (egg cells) that are fertilized by two separate sperm.
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 ...
There is evidence of heritability in personality traits. For example, one study found that approximately half of personality differences in high-school aged fraternal and identical twins were due to genetic variation - and another study suggests that no one personality trait is more heritable than another. [6] [8]
The Minnesota Center for Twin and Family Research (MCTFR) is a series of behavioral genetic longitudinal studies of families with twin or adoptive offspring conducted by researchers at the University of Minnesota. [1] It seeks to identify and characterize the genetic and environmental influences on the development of psychological traits.
Take a look at how genetically similar we are to everything around us: For humans, we're 99.9 percent similar to the person sitting next to us. The rest of those genes tell us everything from our ...
The use of twins can improve the statistical power of a genetic study by reducing the amount of genetic and/or environmental variability. [1] " Identical twins" (monozygotic (MZ) twins) share virtually all their genes with each other, and "fraternal twins" (dizygotic (DZ) twins), on average, share about 50% of their genes with each other (about the same amount of sharing as non-twin siblings).