Author Topic: GEDmatch HELP PLEASE  (Read 743 times)

Offline RossGillbanks

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GEDmatch HELP PLEASE
« on: Friday 05 March 21 14:06 GMT (UK) »
I have done an autosomal DNA test Via Ancestry. Trying to figure out if there is a relation between myself and user JimGillbanks. He did not show as a match on Ancestry,

However when I done a one to one comparison on GEDmatch and lowered the segments to 3 cM We do share some DNA.

The problem is we wouldn't match on Ancestry as the largest segment we share is under 6 cM (Ancestry's matching threshold to my knowledge).

I am going to try and locate a yDNA test as we both descend down a paternal line from both our tree's. In the meantime could anyone tell me if this match holds any significance? The reason I cannot rely on genealogy research is due to a brick wall on my side around the early 1800's. Which is proving near impossible to break through.

Any advice is much appreciated and results from GEDmatch below;

Largest segment = 4 cM

Total Half-Match segments (HIR) 16.8cM (0.47 Pct)

5 shared segments found for this comparison.

427847 SNPs used for this comparison.

52.315 Pct SNPs are full identical
 

Offline devondaenys

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Re: GEDmatch HELP PLEASE
« Reply #1 on: Sunday 07 March 21 00:36 GMT (UK) »
My first question to you here is- how many generations back do you think this genetic connection might be? Because once you've gotten 5 generations back (great-great-great grandparents), there's a decent chance that you may not have inherited any DNA from an ancestor. However, of course, this doesn't mean you and another person aren't family! It just means this particular person's DNA (or at least, a notable portion of it) didn't manage to make it to both of you. And when you think about how many more people would've married into the family within that (5 generation) time, it's totally understandable.

Now for the real science. Essentially, once you get down to 2cm, you're fairly likely to be looking at ANCIENT dna. As in, everyone-ultimately-came-from-Africa or Ghengis-Khan-had-how-many-kids level ancient. So basically, not something you should even remotely rely on when doing genealogical research. You've probably heard the 'fun fact' that all humans share 99% of their DNA. While that's not an exact, universally accurate statistic, there's a kernal of truth to the general idea... which is why most DNA companies have a 5-10cm cutoff. In fact, GED match has been pretty notorious for giving false positives, simply because it allows its users to lower their threshold so much. Most companies have good reason for not doing that! Some people have actually done little experiments with GED: once they lower their threshold to 2cm, they suddenly become 'related' to a fifth or so of the site's users!

In sum--- No, it is not a significant relationship, nor telling evidence of one. BUT: as I explained in my first paragraph, you and this person might very well be family, even if your DNA doesn't match up as such. So this is certainly not a reason to give up on the possibility of a relationship! But perhaps it's time to take a step back from DNA and focus on records/research. Good luck to the both of you :)