Will DNA Testing confirm if I am related to another person?

[pandacub]

I am trying to understand how DNA Testing works but I have to admit to being thoroughly confused so I hope someone will be kind enough to help me.

My situation is that my Paternal GreatGrandfather was illegitimate.  I know from his birth cert and baptism record that his father was Philip Small.  My research has led to me to a Philip Small from Dundee 1845-1931, who I suspect could be my 2 x GreatGrandfather. 

I have made contact with a person who is a direct descendant of Philip Small from Dundee, and  had also come to the conclusion that my GreatGrandfather could be the illegitimate child of their ancestor.

We are both happy to pay for DNA Testing but are unsure if it would definitely confirm if we share the same ancestor or not?

Many thanks.

[LizzieL]

If you have a DNA match with the other person it will certainly confirm you are related in some way and share an ancestor somewhere. The amount of shared DNA gives an indication of the closeness of the match,
This is useful to predict possible relationships
https://dnapainter.com/tools/sharedcmv4

If you and the other person are of the same generation and share a 2 x great grandfather (but have different 2 x great  grandmothers) you would be half third cousins. To definitely identify the shared ancestor, you would also need to look at matches you both share, as you could share a different ancestor from the one you are expecting.

[pandacub]

Thanks very much LizzieL.  It sounds as if the DNA test will definitely be worth taking.  One more question please.  I've seen adverts from various places for the tests, is Ancestry the best one?

[LizzieL]

I took the Ancestry one and I think most people on here would also recommend Ancestry as they have the largest number of people on their database, so more likely to get large numbers of matches. You can also link a tree to your results. Ancestry can also find common ancestors for you by comparing trees - but beware that is based on your matches' trees which may have errors in them.
I have a half third cousin, who is obviously related because we have a lot of shared DNA, but Ancestry doesn't pick up our common ancestor, because she has a big mistake in  her tree (wrong 2nd wife for my 2 x great grandfather). Another common ancestor that Ancestry picked up for me is the wrong relationship, because my match's tree shows my 3 x great grandmother's brother as her father.
It is also possible to download your raw DNA data from Ancestry and upload to a number of other sites (Gedmatch, My Heritage etc) and so increase chances of matches with people who originally tested with other providers.

[pandacub]

Great, thanks very much LizzieL.  I've so far avoided the Ancestry trees as I've heard about so many inaccuracies with them. I initially just put my tree on TheGenealogist as I like their system of people having to request access to view, that way I can explain about the bits of my tree that I'm not sure about.  I've not made many contacts from TG though and Ancestry certainly seems to have a bigger database.  So perhaps I need to think again.

Thanks again for all your help, much appreciated.

[LizzieL]

You can always make your tree private on Ancestry, but make it searchable so that if people find a possible common ancestor they can send you a message. Then you can either provide them with information or just allow that one person access to view - or, of course,  tell them your John Smith born 1800 in Gateshead cannot possibly be the same as their John Smith born 1870 in Cornwall 

[LizzieL]

Ancestry having a sale at the moment but ends 11.59 pm tonight

https://www.ancestry.co.uk/c/dna/offer?o_xid=123120&o_lid=123120&o_sch=Email+Campaigns

They usually have a sale around Black Friday as well

[pandacub]

Thanks, I didn't know the Ancestry trees could be private, sounds a good option for me, especially with the current sale.  I think I was put off the Ancestry trees when a neighbour showed me her family tree which she had constructed during a 14 day trial with Ancestry.  There were glaring errors, I could see straight away that someone had lived to 130, someone else had got married at the age of 4 and a 70 year old woman had given birth.  I asked my neighbour about checking sources but she didn't know what I was talking about.  I have politely declined her offer to help me with my tree!

[Biggles50]

I was in the same situation, my Great Grandmother does not have a Father on her Birth Cert and on her Marriage Cert her Grandfather is listed as her Father.

Then I had a 240cM match show up on Ancestry, the match did not respond to a Message and his Family Tree was just two, but one was his Father’s forename and birth date.  I built a tree and found his Great Great Grandfather was the right age to have Fathered my Great Grandmother.

Using the DNA Shared Match’s tool give my match a 2C relationship and other DNA matches to this new line all have a relationship to me in the range of Probabilities in DNA Painter.

My confirmation will be if the DNA results of a first Cousin match’s my own,

So yes DNA does work but if you have a first Cousin who you share this Great Grandfather with or even a Second Cousin you could get them to test as well and they too should share with the direct descendent of Philip Small thus giving extra confidence in your research