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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 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.
[1] [2] The genetic difference between the offspring and the parents, but the similarity among siblings, are significant distinctions between polyembryony and the process of budding and typical sexual reproduction. [2] Polyembryony can occur in humans, resulting in identical twins, though the process is random and at a low frequency. [1]
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]
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 8-year-old identical twins from Los Angeles have quickly amassed quite the internet following -- over 1.5 million on Instagram, to be exact! -- thanks to their gorgeous looks.
Twins are concordant when both have or both lack a given trait. [1] The ideal example of concordance is that of identical twins, because the genome is the same, an equivalence that helps in discovering causation via deconfounding, regarding genetic effects versus epigenetic and environmental effects (nature versus nurture).