DNA and Genealogy

I was recently reading a post by Judy Russell, the Legal Genealogist, on DNA, and how the results of a test can be misinterpreted.  I've been thinking about doing a DNA test recently, and found her blog post absolutely fascinating.  I have included a link to it above.

Judy gives two examples of how the results of a DNA test can be misinterpreted.  Firstly - identical twins.  Because the DNA of identical (NOT fraternal) twins is the same, the children of both twins will share sufficient DNA to appear as siblings, and will share enough DNA with their parent's identical twin for them to show as parents.  So if your mother is an identical twin, her identical sister will show as a parent match, and that identical sister's children, your cousins, will show as sibling matches.  Just imagine the trouble misinterpreting those results could cause!

The second example is one I never would have considered.  If the person tested has ever had a stem cell or bone marrow transplant, then the autosomal DNA will match the donor, NOT the person's biological parent.

I know a number of people who have has a DNA test with one company or another, and for most of them the experience has been a positive one and the results have been approximately as anticipated.  There have, however, been a few people I know who have been surprised - or quite rudely shocked - by their results.  One friend (who has given me permission to refer to his results) turned out to NOT be a DNA match to the man he had always thought to be his father.  This was something both his parents has been aware of, but he had not.

While 'unexpected' results to a DNA test seem fairly rare, they are always a possibility - just as when researching your family history there will sometimes be surprises, shocks and scandals.  We all need to be aware of this - and be prepared to accept that our ancestors may have been fallable, our family stories may not be 100% accurate, and that every family has the occasional black sheep.