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Identical Twins Test 5 DNA Ancestry Kits, Get Different Results On Each (www.cbc.ca)
Freshly Exhumed writes: Uh-oh, something is not right with the results of most popular DNA ancestry kits, as a pair of identical twins have found. Charlsie Agro and her twin sister, Carly, bought home kits from AncestryDNA, MyHeritage, 23andMe, FamilyTreeDNA and Living DNA, and mailed samples of their DNA to each company for analysis. Despite having virtually identical DNA, the twins did not receive matching results from any of the companies. "The fact that they present different results for you and your sister, I find very mystifying," said Dr. Mark Gerstein, a computational biologist at Yale University. Gerstein's team analyzed the results, and he asserts that any results the Agro twins received from the same DNA testing company should have been identical. The raw data collected from both sisters' DNA is nearly exactly the same. "It's shockingly similar," he said.
They're IDENTICAL twins, right? Why would their DNA be "virtually" the same? Why would there be ANY level of shock with that? ELI5 please.
Because, for each test, there are some SNPs that the lab is unable to determine ("no-calls"). But these are going to be different for each individual, and in fact for each test an individual takes.
There also are likely to be a very small number of SNPs that are simply read incorrectly.
Because of these two issues, the raw results for the two identical twins will almost certainly not be the same -- although the results would have been identical if they had been able to get (correct) results for every single SNP.
Measuring DNA results is always an exercise in statistical analysis. Mitosis does not produce exact copies. Every cell division has changes from its "parent" cell. When labs test your DNA, they rely on a large sample size, and calculate averages. Your results at a specific location might be 65% AA and 35% TT. They are going to show a result of AA in this case.
DNA results ARE meaningful, but it is necessary to understand what the results, and the algorithms, actually mean before making conclusions from them.
I've been tested by 3 labs; several hundred (of 700,000+) of my results differed between the three labs. When this happens, we geneticists throw out the mismatches as errors. I've never seen this change any results in a meaningful way.