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  2. Twin study - Wikipedia

    en.wikipedia.org/wiki/Twin_study

    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).

  3. Twin - Wikipedia

    en.wikipedia.org/wiki/Twin

    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 ...

  4. Zygosity - Wikipedia

    en.wikipedia.org/wiki/Zygosity

    Fraternal twins are dizygotic because they develop from two separate oocytes (egg cells) that are fertilized by two separate sperm. Sesquizygotic twins are halfway between monozygotic and dizygotic and are believed to arise after two sperm fertilize a single oocyte which subsequently splits into two morula .

  5. Multiple birth - Wikipedia

    en.wikipedia.org/wiki/Multiple_birth

    A multiple pregnancy from a single zygote is called monozygotic, from two zygotes is called dizygotic, or from three or more zygotes is called polyzygotic. Similarly, the siblings themselves from a multiple birth may be referred to as monozygotic if they are identical or as dizygotic (in cases of twins) or polyzygotic (for three or more ...

  6. Twins and handedness - Wikipedia

    en.wikipedia.org/wiki/Twins_and_handedness

    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.

  7. Monochorionic twins - Wikipedia

    en.wikipedia.org/wiki/Monochorionic_twins

    Various types of chorionicity and amniosity (how the baby's sac looks) in monozygotic (identical) twins as a result of when the fertilized egg divides. Monochorionic twins are monozygotic (identical) twins that share the same placenta. If the placenta is shared by more than two twins (see multiple birth), these are monochorionic multiples.

  8. Falconer's formula - Wikipedia

    en.wikipedia.org/wiki/Falconer's_formula

    Falconer's formula is a mathematical formula that is used in twin studies to estimate the relative contribution of genetic vs. environmental factors to variation in a particular trait (that is, the heritability of the trait) based on the difference between twin correlations. [2]

  9. Heritability - Wikipedia

    en.wikipedia.org/wiki/Heritability

    Fraternal or dizygotic (DZ) twins on average share half their genes (assuming there is no assortative mating for the trait), and so identical or monozygotic (MZ) twins on average are twice as genetically similar as DZ twins.