The Importance of Zygosity Testing

For research purposes, scientists need to distinguish between MZ and DZ twins. If they are studying genetic influences on health, it is very important to know if they are working with twins who share the same genetic make-up.

For twins themselves, the biggest reason might be curiosity, or to know the answer to the common question, “Are you identical or fraternal?”


As with any family member, you might also be curious about how your twin’s health relates to your own health. In addition, you might eventually encounter some medical situations where knowing your zygosity could be important. For example:

  • If one twin needs an organ transplant, the best donor would be his or her MZ twin, since there is an extremely low chance of organ rejection.
  • If one twin needs a blood donation, his or her MZ twin would be the perfect blood donor since both twins have identical blood types.
  • If one twin is diagnosed with certain diseases, the chance that the other twin might eventually have the same disease is high if they are MZ twins. Depending upon the disease, doctors can suggest possible ways to prevent it in the unaffected twin, or they may be able to test for the disease to diagnose it early and avoid possible complications.

If you would like additional information about how zygosity findings might affect your personal health, contact your health care provider or a genetic counselor. Genetic counselors may be located through the National Society of Genetic Counselors or the American Board of Genetic Counseling.