Understanding FamilyFinder (autosomal testing)

Understanding FamilyFinder (autosomal testing)

By Cathy Roberts

2/10/2012

Some of our project members have expressed an interest in FTDNA's mtDNA and FamilyFinder testing. Since the Phelps project is strictly YDNA we rarely comment on anything else. To be helpful to those who are interested on other testing, below is a wonderful explanation of the several tests written by Cathy Roberts.

Along with their YDNA and mitochondrial DNA (mt-DNA) tests, Family Tree DNA also offers "Family Finder" tests which is autosomal DNA (atDNA) testing. While all three are useful DNA tests, they're very different. With YDNA testing, the results are pretty much absolute. If the male testee matches with another man, then that shows that they are related (the degree to which they're related can vary a lot, but they do match). If there's no match, then they're not related.

With atDNA testing (FamilyFinder), not having a match with someone does not mean that you're not related - except in cases where you and say, a first cousin get tested, and don't match at all. At that degree of relationship, you will share DNA, so not matching a known first cousin means that there're some juicy details in someone's parentage. Even when it's reported that you are a predicted match to another person, if the predicted match is a distant one, then it could be a false match - where it's just coincidence that you and that other person have a segment of DNA that is the same (referred to as being "Identical by State" versus being "Identical by Descent"). Or, it can mean that that particular bit of DNA is one that can pass from generation to generation without recombining, and you are related. With atDNA testing, having a good and solid paper tree, with as many collateral lines as possible is almost a necessity.

For someone new to these kinds of tests, trying to understand them and what the matches mean can be hard, since you're being bombarded with matches from many sides.

The main thing to keep in mind is that YDNA testing and mt-DNA testing test Short Tandem Repeats (STRs). atDNA testing (FamilyFinder) tests Single Nucleotide Polymorphisms (SNPs). SNP testing cannot determine a man's YDNA, and YDNA testing cannot determine matches from anyone other than the father, grandfather, etc. The one area where SNP testing is used with those who have taken the YDNA test is if they want a confirmed haplogroup). With YDNA testing, a father and son can be tested, and all the results will show is that they're an exact match and closely related (although a man's YDNA could change or mutate as he passes it on to his son). The results cannot tell if they are father and son.

With atDNA testing, the results can get a bit closer to telling you how you're related to a match, but even then, it's not exact. Children inherit atDNA from their parents within a certain percentage range (50% from each parent). So, parent/child matches are often easy for the computer to find. Cousin matches can be more iffy, as the computer usually can't tell a difference between a 2nd cousin and a 2nd cousin, once removed. Uncle/nephew or uncle/niece matches are usually spot on, but sometimes they might not share enough DNA for that, and it might be reported that the match is anything from uncle/nephew to 1st cousin. I've connected with some distant cousins at a different DNA testing company, not because we have atDNA in common, but because we had similar surnames in our profiles. Our atDNA did not match. If my parents were still alive, then it could be possible that the person would have matched my parents, and that the reason we didn't match is because I didn't inherit the matching atDNA from a parent.

Overall, after 5 generations, the amount of atDNA that you inherit from a particular ancestor becomes smaller and smaller. Siblings, outside of identical twins, do not inherit the exact same DNA from their parents. Each sibling can get a little bit different parts of DNA than the others. Of the three tests - YDNA, mt-DNA and atDNA testing, mt-DNA and atDNA testing can be the most frustrating. With mtDNA, your 'close' match and you could very well share an ancestor who was alive anywhere from 500 to 1000 years ago. With atDNA testing, you and the other person both have a large batch of ancestors to look at. If you don't know enough of them far enough back, then you might not ever find your common ancestors. And then you've got the probability of what they call a 'non-parent event', where one (or both of the parents) is not a biological parent. In the old days, informal adoptions were rather commonplace, especially if the people lived in more rural areas. Other things that can cause frustration are where your match is in another country, and you've researched further back in the U.S. than they have in England; or you and your match are related in more than one way.

DNA Forums (www.dna.com) has some good explanations on the various DNA tests, and most of the time, the answers aren't too technical. Family Tree DNA has some pretty good articles on their site that explain matching with atDNA and they also have a message board/forum, where you can read past messages/questions about what makes a match. Reading the posts at either site, even if the topic might not seem to pertain to your particular results, might still give you some insight as to what to expect with the various tests.

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