Heteropaternal Siblings Misclassified as Dizygotic Twins: A Potential Biasing Factor for Heritability Estimates?

Heteropaternal superfecundation (HP) occurs when two or more ova are fertilized by sperm from separate males. The resulting siblings are genetically equivalent to half-siblings and share, on average, 25% of their inherited genetic material. In the absence of genetic testing HP siblings could be treated as dizygotic (DZ) twins in behavioral genetic analyses and bias heritability estimates in phenotypic decomposition models. However, the extent to which such misclassification could affect calculated estimates of heritability is currently unknown. Employing simulation analyses, the current study assessed the potential biasing impact across a variety of conditions varying by proportions of DZ twins, sample sizes, and low, moderate, and high levels of genetic and environmental contribution to phenotypic variance. Overall, the results indicated that misclassified HP siblings had minimal impact on estimates of heritability. Nonetheless, greater attention should be paid to the identification of HP siblings within existing and future twin datasets.