Identical triplets should have identical DNA, right? That is what Dr. David Ku of Universal Genetics told Inside Edition. Inside Edition used three sets of identical triplets and one rare set of identical quadruplets to test DNA ethnicity reports from 23andMe, Family Tree DNA, and AncestryDNA. The results are a rude awakening.
(Select any image in this article to see the Inside Edition video on YouTube.)
One McGraw triplet in the 23andMe test had twice the amount of French and German ancestry as another. According to Family Tree DNA, British Isles ancestry in the Maynard triplets ranged from as low as 59% to as high as 70%. The AncestryDNA test returned a range of British ancestry differing by just 2%. The 23andMe results for the Pyfrom Quads, was the best, giving identical ethnicity.
First the idea that identical twins have identical DNA has been called into question in recent years. Last July, a scientist writing for the BBC said that mutations occur in DNA fast enough that “between 10 and 100 new mutations per person…occur early enough in embryonic development to be present in most cells in the body.” Keep in mind, however, that there are 3 billion base pairs. (See “Do Identical Twins have Identical Genes?” in Science Focus, The Online Home of BBC Focus Magazine.) A March 2008 article in The American Journal of Human Genetics reported a scientific study showing that DNA in identical twins is not identical. Something called copy-number variations can cause their DNA to diverge in material ways. (For a layman’s discussion of this study, see “Identical Twins' Genes Are Not Identical” in Scientific American.) Can these differences explain the results found by Inside Edition? I don’t know. It has been known for a while that epigenetics cause variations in identical twins, but epigenetics don’t change the underlying DNA.
Second, it is possible that fraternal twins can look very similar. Particularly when young, it may require a DNA test to distinguish monozygotic (identical) and dizygotic (fraternal) twins/triplets/quadruplets. One of a couple of the triplets in the Inside Edition broadcast look different enough in the broadcast that to me they could conceivably (unintentional pun) be fraternal. Inside Edition did not disclose the estimated relationships found among them.
Third, the testing companies can’t control how carefully test takers follow instructions and avoid contamination. I imagine there are many common substances in our homes, our food, maybe even our water, that have the ability to contaminate a DNA sample. Can such contamination explain the differences found by Inside Edition?
Someone with more molecular biological knowledge than I have will have to weigh-in on what might explain the large differences seen among triplets in the Inside Edition test.
For more information, see “How Reliable Are Home DNA Ancestry Tests? Investigation Uses Triplets to Find Out” on the Inside Edition website.