Question about DNA tests

[t_huff]

Hi everyone,

I am helping my father with this project.  He took the 12 marker test and now is in the process of upgrading to the 25 marker test.  I hope this isn't a dumb question, but when the test results are compared to, say, the test results of someone by the same surname that was born maybe in the 1700's, how do they come by those DNA results for the long deceased person? 

[t_huff]

Okay, after I posted my question, I saw where this question was addressed in another post.  But I still question something.  If you test a descendent of someone who was born back in 1700's in an attempt to obtain their ancestor's DNA, what if that person is incorrect about the relation?  We all know that genealogy can be tricky and sometimes people make quantum leaps about who their ancestors are.  That would mean that the DNA posted for the ancestor is correct if the person is a true descendent.  Is there any qualifying criteria?  Do they have to be able to prove their ancestory -- or am I somehow missing something?  I'd appreciate any input.

[Biscuits]

This is from our FAQ, which partially addresses your question:

What if I get back results I don't like, such as indications of a non-paternity event?

Non-paternity results did occur and they may be obvious through DNA testing when the result is being compared in a well-documented family. 

There are several scenarios that fit into the category of non-paternity event.  One, of course, is infidelity, while another common event was the unrecorded adoption.  As there were many adult deaths on the frontier, children were frequently raised by relatives or friends, with the adoptive parents giving the child their own last name.  Where infidelities or adoptions have long been rumored and now proven, there can be some satisfaction.  Where an infidelity or adoption occurred in a well-documented family, identifying it helps in clarifying the DNA profile of descendants.  Where the non-paternity event occurs in a family without extensive documentation, it can be very disruptive and prevent the participant from obtaining matches within the surname.
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http://www.worldfamilies.net/faqs.html#What%20if%20I%20get%20back%20results%20I%20don't%20like,%20such%20as%20indications%20of%20a%20non-paternity%20event?

In the end, you are relying on the paper trails of whoever is tested.  A good researcher has kept his source material to make it easy to verify his family tree.  You'd have to ask whoever you get tested for that person's research in order to judge it for yourself.

DNA testing does provide a major boon though - if there are other individuals in the database with matching DNA, you can do a search to find out.  This may help you verify your paper trails to make sure that you actually are getting the results you expect:

How do I compare my results to other people?

Once your results are available, you'll be able to go into your personal page at FTDNA and do a search for yDNA matches.  You'll always see all of the other results in your surname - and at that time, you'll be able to select a preference that allows you to compare against all others of all surnames who opt in to the FTDNA internal comparison.  (When your results are back, we'll post them on your surname project’s Results page.)
You'll also be able to upload your results to Ysearch (FTDNA's public database - open to all) and see who you match there.

FTDNA will send you automated messages when you have a match (either with only your surname project members or to their internal "opted-in" database) - depending on your selection

http://www.worldfamilies.net/faqs.html#compareresults