Dictionary of Human Evolution and Biology

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Twins, Dizygotic

DZTs are siblings thought to be the result of two simultaneous pregnancies such that a pair (or more) of individuals reside in a womb. There are two placentas, and twin pairs can be the same sex or opposite-sexed. Genetically, DZTs are only as similar as ordinary pairs of siblings; they may be discordant for many character states. These twins share half their genes, on average, by descent from the same parents. There is a strong maternal age affect, with the probability of dual conception rising sharply in the latter portion of the 4th maternal decade (Aka binovular twinning). The DZ twin rate varies by geographic region: overall number of DZ twins per 1,000 live births is 2-7; in North America, 7-11; in Europe, 9-20; in Africa, 45-50.

Cf. twins, monozygotic, uniovular dispermatic twins, and half-siblings.

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