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Privacy and Medical Implications of DNA Testing for Genealogy

First, Some of My Own DNA

Before we discuss the meat of the privacy question, let's look at some of my own Y-DNA.  Here are my own first 25 STR (Short Tandem Repeat) Y-DNA markers in standard genealogical order.  The DYS numbers are the locations or names of the marker, and the "allele" values are the number of tandem repeats of the molecular pattern at that location on the Y-chromosome. 

First 25 STR markers from Martin Potter's Y-DNA
DYS # 393 390 19/394 391 385a 385b 426 388 439 389-1 392 389-2
Allele 13 23 14 10 14 16 11 14 11 12 11 30
DYS # 458 459a 459b 455 454 447 437 448 449 464a 464b 464c 464d
Allele 15 8 9 8 11 23 16 21 29 12 14 15 16

These numbers carry no private information and, by themselves, they are not very exciting except perhaps to a geneticist.  Genealogists, however, get excited when they find someone else who matches exactly, and even more excited if the match is based on 37 or 67 markers, rather than just 25.  In my experience matches at the 12- and 25-marker levels are rarely useful, and most genealogists hope to find exact or nearly exact matches at 37 or 67 or even 111 markers.  An exact match at 67 markers is almost always very strong evidence of a close genetic relationship.  Now that's exciting!   So why not get tested and see if you match me or someone else, a lost cousin perhaps? 

Please contact me if you think you might match me or if you are interested in the rest of my Y-DNA markers.  I have been tested for 111 of these STR markers as well as a number of polymorphisms (called SNPs).  In my case the most important SNP is the one called P109 which (so far) defines the ancient ethnic origin or genetic haplogroup of my paternal family line. 


No one can steal your identity by learning the genetic markers of your DNA as are commonly tested for genealogical purposes.   In fact, there is little concern about privacy at all because it would be very difficult to use the standard genetic tests of genealogy to uniquely identify anyone.   Dozens, even hundreds or thousands of other men share these exact same genetic markers.   Keep in mind that when testing 67 Y-DNA "STR" (short tandem repeat) markers, only 67 out of approximately 400 markers are tested.   When testing to confirm or refine the determination of a man's haplogroup (ancient ethnic origin), using tests for specific "SNPs" (single nucleotide polymorphisms), we are testing only a handful of the possible 60,000,000 different nucleotides.   Further, none of the X-chromosome, nor any of the other 22 chromosome pairs, nor any of the mitochondrial DNA is being tested.   So it is really a very small fraction of one's total DNA that is actually examined and revealed.   Would your bank cash your cheque if you gave them the same fraction of your signature? 

Nevertheless, preserving the privacy and anonymity of their customers is a major concern for the reputable DNA-testing companies and you should choose one of them.   For example, in surname projects hosted by reputable companies, the test results are posted anonymously on the Internet and only you, the testing company and the project administrator know which test results belong to you.   The best advice I can give is to choose one of the several companies that are run by scientists, rather than one of the many run by marketing and advertising experts.   Personally, I have used Family Tree DNA for most of my own testing and for all three of my surname DNA projects.   The two other companies I have used, neither of which is still in business as such, are the Sorenson Molecular Genealogy Foundation (SMGF) and Ethnoancestry (which now does busines as BritainsDNA).  I have no interest in any of these companies except as a satisfied customer. 

Medical Implications

With one small and extremely (extremely!) rare exception (an STR marker called DYS464), none of the commonly-tested Y-chromosome markers has been found to have any medical significance, so you need not worry about finding any unwanted or unexpected health-related information from your genealogical Y-DNA test. 

Mitochondrial DNA (mt-DNA), on the other hand, can and sometimes does reveal health-related information, but this kind of DNA is not used in most surname projects because mt-DNA is not inherited along the paternal line, that is, the family line that usually carries the surname. 

A number of companies offer DNA tests specifically for health-related purposes, but the testing company that I use for my own genealogy projects (Family Tree DNA) does not offer these tests. 

The Bottom Lines

1.  If you are testing only the Y-chromosome to find connections with or the ancient origin of your paternal line, there are no privacy concerns

2.  If you are testing only the hypervariable regions (HVR1 and HVR2) of your mt-DNA to find connections with or the ancient origin of your maternal line, there are no privacy concerns

3.  If, however, you are testing the full sequence (FGS) of your mt-DNA there might be some concerns and you should be sure to choose a reputable testing company and upload your results only to proven, anonymous databases.  It is also advisable to have your results assessed by a competent professional, a short list of which can be found at ISOGG, in order to know which mutations of your mt-DNA might contain sensitive information and the medical significance of them.