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Abstract

We developed a zygosity questionnaire for use in young twins and assessed its validity using the results of DNA diagnosis. The participants were divided into two groups: 105 pairs of adolescent twins (12-16 years old), 47 pairs of child twins (2-12 years old), and their respective parents. The DNA diagnosis of zygosity was made with polymarker polymerase chain reaction (PCR) amplification of five loci, using the AmpliType PM PCR Amplification and Typing Kit; this method has an accuracy rate of 99.0%. A parsimonious model for each sample was established using stepwise logistic regression analysis of the 20 items of the questionnaire. The total accuracy rate of the model was satisfactory for both parental reports (three items) and self-reports (three items) of adolescent twins (97.4 and 95.6%, respectively), while that for parental reports on child twins (two items) was less satisfactory (92.5%). For adolescent twins, if DNA diagnostic workups were limited to those with discordant reports either from themselves or from their parents, the accuracy rate increased to 100% for parental reports and 98% for self-reports.

Twinning and major birth defects, National Birth Defects Prevention Study, 1997–2007

“…11 12 Information on zygosity is particularly difficult to obtain, as the gold-standard for determining zygosity is genetic analysis. 26 Even self-report of zygosity from parents is not a reliable source of information on zygosity. 27 However, our simulation modelling approach may be a useful alternative to the more rudimentary sex-pair analysis for like-sex twins, as the uncertainty caused by the potential misclassification is taken into account.…”

Learning to do well or learning to do good? Estimating the effects of schooling on civic engagement, social cohesion, and labor market outcomes in the presence of endowments

“…Twins were asked a series of questions designed to evaluate their zygosity, including questions regarding shared physical characteristics. Although physical similarity is by no means a perfect indicator of zygosity, studies reveal a high level of concordance between indicators based on reports of appearance (e.g., whether they look as similar as “two peas in a pod”) and indicators based on definitive molecular tests (Chen et al 1999). After eliminating observations with incomplete information, the final maximum sample consists of 3,023 unrelated persons, 1,366 siblings (including some in the national sample), and 1,588 twins, of whom 954 were fraternal (dyzygotic, DZ) and 634 identical (monozygotic, MZ).…”