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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 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 ...
Unlike monozygotic twins, dizygotic twins result from the fertilization of two eggs by two separate sperms within the same pregnancy. This causes the set of twins to have genetic variations, so their genetic information is unique from one another. In studies conducted between 1924 and 1976, there were more left-handed monozygotic twins.
Even two organisms with identical genotypes may differ in their phenotypes, due to phenotypic plasticity. To what extent a particular genotype influences a phenotype depends on the relative dominance, penetrance, and expresivity of the alleles in question. One experiences this in everyday life with monozygous (i.e. identical) twins. Identical ...
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 ...
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).
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.