Zygosity questionnaires have been developed to determine the zygosity of a pair of twins based on their overall similarity (“as alike as two peas in a pod”) and how often they are confused by other people.

TRA has a Peas-in-a-Pod questionnaire with three questions:

The questionnaire is based on research by S Ooki and can accurately determine zygosity for 93% of twin pairs:

TRA have separately validated this questionnaire:


Twins Research Australia

Address: 3/207 Bouverie St
Carlton, Vic 3010

Email: info@twins.org.au

ABN: 84 002 705 224

Twins Research Australia has received continuous funding from the National Health and Medical Research Council (NHMRC) since 1981, most recently through a Centre of Research Excellence Grant (2015-2022). TRA is administered by the University of Melbourne.

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