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Identical Triplets

January 11, 2007

A listener asks: Are identical triplets possible?


Three of a kind. I’m Bob Hirshon and this is Science Update.

Inquiring mind Michael Mikkalo of Washington, DC, has heard of identical twins, but wants to know whether there are identical triplets. We asked clinical geneticist Carol Greene of the University of Maryland Medical Center.

CAROL GREENE (University of Maryland Medical Center):
Yes, there are identical triplets. Once you have fertilization, you have what we call a zygote, and if the zygote splits, you can have two identical individuals, and that would be identical twins. And if there’s another split then you could have identical triplets.

As you can imagine, this is very rare. According to one estimate, only about 150 sets of identical triplets are born in the United States each year.

If you have a science question, call us at 1-800-whyisit. If we use it on the air, you’ll win a Science Update mug. I’m Bob Hirshon, for AAAS, the science society.