What is proven in DNA test?

+6 votes
147 views

If I take a DNA test, what does itprove or how does it prove anything about my ancestors that lived in the 1600's or the 1700's? How many generations does any information go back? Does this test help me discover my family? Thank you, Jerry (Dolman-113)

in Genealogy Help by Jerry Dolman G2G6 Pilot (167k points)

3 Answers

+5 votes
 
Best answer
A Y-DNA test can confirm your direct paternal lineage and has no limitation on generations. An autosomal DNA test is generally good for about five generations and will provide matches up all of your family lines -- both male and female.  I have matched people as far back as seven generations via autosomal.

DNA tests can be a huge help to help you trace your ancestry and find previously unknown cousins.  It can confirm family connections where no paper trail exists.  If you have one or both parents alive, I recommend having them tested first.  That will take you back another generation as well as providing additional matches. They can share DNA with someone that you don't.  Plus it will help you identify which side of your family you are matching people on (if you test both yourself and your parents).

You do need to have put together a family tree to be able to determine your most recent common ancestor with matches.
by Darlene Athey-Hill G2G6 Pilot (428k points)
selected by Jerry Dolman
+9 votes
by Kay Wilson G2G6 Pilot (183k points)
+2 votes
Consider for a moment that none of your ancestors had their DNA tested. Your DNA can only suggest a connection with somebody else who had their DNA tested when certain relatively conserved areas are identical. If it is Y-chromosomal DNA this suggests that the two individuals had a patrilineal ancestor in common, if it is mtDNA it would be a matrilineal ancestor. It does not indicate who the ancestor is, that can be inferred from pedigree charts. If both individuals had John Doe in 1650 as a paternal ancestor it is very likely that he indeed is their common ancestor. Disproving ancestry on the other hand is certain: If two people have the same paternal ancestor in their pedigree but their Y-chromosomal DNA is different it is certain that one of them is mistaken in their belief in a biological relationship.
by Helmut Jungschaffer G2G6 Pilot (542k points)

DNA does more than 'suggest' a connection.  It can prove a connection, because DNA doesn't lie.  If you share a large segment of DNA with another person, it proves that you and that person have a common ancestor (CA).  Finding the common ancestor isn't always easy, though.  That is when triangulated groups are so helpful.  (For those who might not know what a triangulated group is, that is when you share a common segment on a chromosome with two or more people.)  When you have three or more of you with the common segment, it can help identify the MRCA (most recent common ancestor).  Regardless of whether you ever figure out the CA or MRCA, if you have a large common segment then you know you have a common ancestor.

Granted, the below referrenced statement of The American Society of Human Genetics is 6 years old and some of the issues addressed have shown incremental improvement since, but the underlying statements on methodology hold. The operative words are "ancestry estimation" and "inference", not "proof".

http://www.ashg.org/pdf/ASHGAncestryTestingStatement_FINAL.pdf

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