Why are there more same-sex than opposite-sex dizygotic twins?

Kanazawa, Satoshi; Segal, Nancy L.; Meza, David de

doi:10.1093/humrep/dey046

Cited by 7 publications

(6 citation statements)

References 32 publications

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“…Our twin sample showed a MZ:DZ ratio of around 1:1, which is unbalanced as compared to the 1:2 ratio observed in the general population (Aston et al, 2008). This situation is consistent with the fact that, although twin cohorts in the Italian Twin Registry (ITR) are identified by applying a population-based strategy within local municipalities (Medda et al, 2019), subjects’ participation in ITR studies still relies on a strong voluntary basis, and it has been previously reported that MZ twins are likely to be over-represented in volunteer samples (Kanazawa et al, 2018; Rushton et al, 2008). In this respect, it may also be interesting to highlight that a MZ:DZ ratio close to 1:1 may even have, in some cases, beneficial effects on statistical power in the context of twin analyses (Visscher, 2004).…”

Section: Discussionsupporting

confidence: 72%

Genetic and Environmental Architecture of Five Factor Model and Super-Factors: An Italian Twin Study

et al. 2021

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No previous research explored the genetic and environmental structure of Big Five dimensions of personality and higher-order factors in a single twin study, except, in part, for just one study. We used the twin design to estimate the effects of genes and environment on both Five Factor model and related second- and third-order factors (i.e., Alpha [stability], Beta [plasticity], and GFP [general factor of personality]). We analyzed data from 314 adult twins (157 pairs: 83 monozygotic, 74 dizygotic; mean age: 52 years) enrolled in the Italian Twin Register. Participants underwent clinical and instrumental evaluations, and completed a 25-adjective list drawn from the Short Adjectives Checklist to Measure Big Five (SACBIF). We applied quantitative genetic models to unravel the sources of variation and covariation for the Big Five and higher-order factors. We found a similar etiological architecture across the different levels of analysis, with moderate to substantial non-additive genetic and unique environmental influences on all the personality traits, and no shared environmental contribution for any of them. We also detected significant genetic correlations for the Big Five dimensions and the Alpha and Beta super-factors. With some limitations, our results suggest that the etiological architecture of personality may be invariant to the factor level of analysis.

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Section: Discussionsupporting

confidence: 72%

Genetic and Environmental Architecture of Five Factor Model and Super-Factors: An Italian Twin Study

et al. 2021

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“…This is not consistent with Weinberg's differential rule, which states that DZ twins are equally likely to be of the same or opposite sex [15]. Possible explanations for this discrepancy are that the CNTR is not a birth registry or that real-world data may deviate from this assumption of independence of sexes within DZ twin pairs [16].…”

Section: Zygosity Determinationmentioning

confidence: 62%

The Chinese National Twin Registry: a ‘gold mine’ for scientific research

Gao

Cao

et al. 2019

J Intern Med

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The Chinese National Twin Registry (CNTR) currently includes data from 61 566 twin pair from 11 provinces or cities in China. Of these, 31 705, 15 060 and 13 531 pairs are monozygotic, same‐sex dizygotic and opposite‐sex dizygotic pairs, respectively, determined by opposite sex or intrapair similarity. Since its establishment in 2001, the CNTR has provided an important resource for analysing genetic and environmental influences on chronic diseases especially cardiovascular diseases. Recently, the CNTR has focused on collecting biologic specimens from disease‐concordant or disease‐discordant twin pairs or from twin pairs reared apart. More than 8000 pairs of these twins have been registered, and blood samples have been collected from more than 1500 pairs. In this review, we summarize the main findings from univariate and multivariate genetic effects analyses, gene–environment interaction studies, omics studies exploring DNA methylation and metabolomic markers associated with phenotypes. There remains further scope for CNTR research and data mining. The plan for future development of the CNTR is described. The CNTR welcomes worldwide collaboration.

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“…1 Among the total dizygotic twins, approximately 40% are opposite-sex (OS). 2 Androgens, particularly testosterone, serve important functions in early embryonic development. 3 Testosterone production in fetuses increases from 8 to 24 weeks of gestation and reaches maximal level between 10 and 15 weeks.…”

Section: Introductionmentioning

confidence: 99%

“…The incidence of spontaneous dizygotic twinning occurs between 1% and 4%, which might be increased by advanced maternal age and the application of assisted reproductive technologies 1 . Among the total dizygotic twins, approximately 40% are opposite‐sex (OS) 2 …”

Section: Introductionmentioning

confidence: 99%