»  How accurate is DNA testing for the purposes of determining twin zygosity?  (Back)

DNA testing is the best available method for determining the zygosity of multiples. After collection of samples, DNA is extracted. The DNA samples are then amplified using 8 or more well characterized DNA markers. These markers are detected using a chemical reaction called polymerase chain reaction (or PCR). The PCR product is then evaluated using a genetic analyzer, which plots each amplified marker. The profiles are then compared side by side. If the twins' genetic patterns are exactly the same on all markers tested, the twins are identical, or monozygotic, with a greater than 99% probability. If the genetic patterns differ from one another on two or more markers, the twins are dizygotic.

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