Early adverse environments and genetic influences on age at first sex: evidence for gene × environment interaction.
Zygosity diagnosis has been performed in 79 pairs of twins using three methods. Simple sequence repeat length polymorphism (SSLP) analysis allows an efficient classification (MZ or DZ) with only a few markers following a simplified technique of extraction and amplification. A method based on a full questionnaire completed by parents about twin similarity correctly classifies 97.46% of the pairs; 92.41% are correctly classified using only four questions as suggested by logistic regression analysis. The third method, using dermatoglyphic analyses, correctly classifies 86.76% of pairs. To lower the cost of DNA diagnosis we stress the possibility of limiting its use to pairs with scores in the overlap area between MZ and DZ twins with a validated questionnaire.