Question

DNA test, so how do I search for relatives with my mt dna from familytreedna? I’m finding it a bit confusing!

Answer 1

It could be used to exclude candidate relatives who have also taken the test and do not match. It could also be used to identify a world region where your direct maternal ancestor from 500 years ago may have lived. But due to very low chance of mutations in each generation, mtDNA (unlike Y-DNA) is not useful for matching a MRCA in a genealogical timeframe - you will likely have dozens of matches with same exact haplogroup.  mtDNA may not change at all in over 12 generations. If you have an exact match with another's mtDNA, your MRCA will be within 22 generations or 550 years!

Comments

And many feel that FTDNA's stated confidence level of 95% for 22 generations to a common ancestor for an exact match of mtDNA full sequencing is a bit over-optimistic. Maybe more than a bit.

I agree with Mike that mtDNA is useful as negative evidence, to exclude hypothetical family lines. But it really isn't much good as a form of positive evidence. We aren't actually testing germline mtDNA--what is actually passed down generation to generation; we can't test that because the oocytes form while the mother is still a fetus herself--and we all have around a quadrillion somatic--body cell--mitochondria happily existing, reproducing, and dying within us all the time. No copy machine is that good, and studies have (very conservatively) estimated that over 45% of us carry more than one mitochondrial genome.

Full-sequence testing might show a mother and son not to be a match (see Blaine Bettinger's blog about his experience, separated by a reported genetic distance of 4 from his mother), and I have one woman in one of my DNA projects who has over 110 exact matches to her full-sequence test. So mtDNA can present incorrect evidence in even parental relationships, or imply evidence that might actually be of no positive value for 30 or 40 generations.

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Here's an article suggesting that the assumption of exclusive maternal inheritance of mtDNA could be problematic: https://www.nature.com/articles/d41586-019-00093-1

Answer 2

Art, I have to be upfront with this:

You aren't going to find a lot of relatives with mitochondrial testing. That isn't really the purpose of it. It is best used for confirming ancestors way back along your maternal line. Since your documented maternal line only goes back to your great grandmother, you aren't going to benefit from that at present. Maybe in the future.

What you want is autosomal testing. That tests your 22 regular chromosomes and compares with other people who have tested to see what segments of DNA you share. Generally it will match you with anyone as close as a 3rd cousin, and about 50% of your 4th cousins... and many cousins who are much more distant will also match you. (See: https://isogg.org/wiki/Autosomal_DNA_statistics ). Some of those who match you will have a family tree, and by comparing your tree to their trees, you'll be able to see how your trees overlap, or if there is something suspiciously similar (folks from the same town or the same name, etc...) that's probably worth investigating to find the connection. It's really, really useful.

If you're going to pursue autosomal testing, here's the next bit of advice:

FamilyTreeDNA is one of the worst choices for autosomal testing due to the small database size (~ 1 million). The larger databases of 23andMe (> 10 million) and Ancestry DNA (>15 million) are needed to facilitate easy and useful discoveries. Even MyHeritage (>2.5 million) is a better option. See: https://isogg.org/wiki/Autosomal_DNA_testing_comparison_chart

With those bigger databases, you don't just get more matches, you get better, closer matches. FamilyTreeDNA has its place, but its autosomal "FamilyFinder" test just isn't that useful for for finding autosomal matches. Their database is useful, in that you can import from elsewhere, in order to get segment data. It's also useful if you have a very specific question that could be solved with Y-DNA or mitochondrial DNA. 

US Thanksgiving is sale season for these kits, so buy yourself one each from 23andMe and Ancestry DNA now if you're able.