I am working on a family tree where the paternal side is entirely unknown. I've tried reaching out to the stronger shared matches via the Ancestry messaging service but most are still unread. I've been able to plot out basic trees for the shared matches from what they have posted online themselves and am experimenting with putting their great grandparents into our tree to try to use thrulines to identify more distant matches to try to find where the shared ancestors might be.
For one of the close matches 217 cm are shared. Thrulines suggested a 2nd great grandfather, who having checked the paper trail (census, births, marriages, deaths etc.) looks like the wrong guy (I've read that Thrulines can give rogue results so have been trying to double check them). The name fits, but other aspects, such as children and parent names, dob etc. are wrong. However, I have 3 DNA matches linking to this guy. They are descendents of his siblings (each descends from a different sibling), so theoretically sharing a 3rd GGF. The amount of DNA shared with these matches is very low: 8cm in 1 segment, 9cm in 1 segment and 14cm in 2 segments. The last one I can see one of her ancestors is also related on the maternal side of my tree. I have a good tree on the maternal side and thus far all DNA matches have fitted with the paper trail. Also looking at the shared matches with the 14cm person, they are all on my maternal side except the 217cm match and a very close relative of the 217cm match. There are no shared matches with the 8cm and 9cm people.
I guess what I'm asking is could the two other matches (8cm and 9cm) be matching by random chance because they are so small? Is there an amount of cm that we share with people by chance even if we are not distant cousins?
I find all this DNA stuff so fascinating, but as soon as I feel I'm making sense of things, something like this happens and I realise I really don't understand very much!
Grateful for any thoughts or insights!
As I know nothing about where you have uploaded you DNA but assume that you have tested your DNA with Ancestry as you mention Thrulines I would first suggest you upload your raw data to as many of the other DNA comparison sites as possible to try to get links with as many new matches as possible, not all testers have uploaded their data to Ancestry. These include FTDNA, 23and Me, MyHeritage and Gedmatch. (make sure you read and are happy with the terms & conditions before you upload your data)
If I understand what you have written so far you know (proved) nothing of the paternal line, so in reality the match results you can identify will be on the maternal line, that will enable you to compile a list of “unidentified” matches that will include matches from the male line along with yet to be identified female line matches.
Have you tried triangulation between you any of you known maternal matches and unknown matches to try find the possible paternal line matches by excluding those who match you and a known maternal line match, If all three of you triangulate the unknown match will also be on your maternal side? If only you and the unknown match share the same segment it is possible the unknown match is a paternal match.
In effect using DNA in the same way as using names to work from the known to the unknown
I would also suggest creating quick and dirty trees, i.e. using sources like online trees to build an unchecked data set to provide names to matches. (it goes without saying that any such use requires extra research later to prove the assumptions being made in the quick and dirty tree but it can be helpful if care is used).
As you keep triangulating and discounting maternal matches you will also build a dataset of possible paternal matches and by elimination will eventually produce pointers to the paternal lineage.
Cheers
Guy