For research purposes, we use a form of zygosity determination called “self-report.” This determination uses the responses that you and your twin provided to two questions on the recruitment survey that you completed when you joined the Registry. These questions are “When you and your twin were children, were you as alike as two peas in a pod or of ordinary family resemblance?” and “How often did parents, relative, teachers, and strangers have trouble telling you and your twin apart?”

Based on the answers that you and your twin provided, and comparing your answers with those of other twins in the Registry, we have developed a method that can predict zygosity with about 96% accuracy. We use this “self-report” zygosity to generate the statistics for our website, and to recruit twins for our studies. It is extremely helpful for research and statistical purposes, since this level of accuracy is enough to reflect group trends and tendencies.

You and your twin may have provided DNA for zygosity testing in the past. This was most likely done by spitting into a small container and mailing it back between 2010 and 2012. The goal of this project was to create a bank of DNA samples which will be available to researchers who are working with the Twin Registry. However, the majority of our studies do not currently test for zygosity (whether a twin pair is identical or fraternal). At this time the Twin Registry has no immediate plans to process the DNA for everyone who has provided a sample. The results will only be run if the samples are used in a study that does need to determine zygosity.

If your samples are tested for zygosity by a specific study at any point in time in the future, we will be sure to let you and your twin know when those results are available. At that point, if both you and your twin re-consent to the release of that information, we will then be able to send you the results of the zygosity test. Please note that these results are for research purposes only. If you need a zygosity test done for medical reasons, click here for information on labs that can perform this service.