DNA testing - genetic genealogy

[Nick29]

Hi Nick,

I was not "pushing" David's site - I merely mentioned that he was researching U-152 and thought you might be interested - obviously not, as you has a five minute look and then did a hatchet job.  He has written many interesting papers, and of course he may not be 100% right about everything, but this is what good science is about - looking at something, having an idea about what it means, and then setting out to prove or disprove your hypothesis.

No, that's not the case at all.  I am not disputing the science of DNA - it undoubtedly works - I am just disputing the way it is being used here, and the rather shaky assumptions being made around it, because they haven't looked at the mathematics and population statistics.

In the meantime I have now had a reply from Terry Barton of "Worldfamilies" with regard to Y-DNA matches -

"Hi Carol.  Yes - a match that is 63/67 or a genetic distance of 4 on 67
markers indicates shared ancestry.  I haven't looked at the calculations
lately - and there are a number of parameters that folks adjust in the
calculation - which change the outcome a bit -  but it seems reasonable that
7 or 8 generations is about the 50% probability for the number of
generations back to a most recent common ancestor (MRCA) in your situation.


However - it's very important that you realize that dna matching is not
precise in measuring generations.  The probability for shared ancestry in
this case ranges from a very few generations to something around 20
generations.  7/8 generations is simply the point where as many folks will
be more than 8 generations to MRCA as they will be less than 7

Now - the bit about 128 ancestors is totally irrelevant.  yDNA is very
specific - it is the y-chromosome - which is inherited from a man's father's
father's ... Father's paternal ancestry - that is being evaluated.  yDNA is
a very specific line of inheritance.

But - and this may be what your match is trying to say - you don't know
where that MRCA is on either your line or your match's line by the number of
differences.  You only know that at some point your two paternal lines
coincide into that MRCA.  It's now a paper trail exercise to find who is
your MRCA."

I am of course doing the paper trail and have already indexed more than 2,500 events for Wood/Woods and variants for the three counties which we are interested in, and will continue to look for the elusive ancestor.

Cheers,

Tisy

Again, David was talking about the science, and not the mathematics.   As you know, every time you go back one generation, you double the number of people at the bottom of the tree.   A seven generation tree contains 128 people at the bottom of the tree.  A 20 generation tree would contain 1,048,576 people at the base of the tree.  The stumbling block is (and always will be) that as you go further back in time, the number of people in the world decreases, and the further you go back, the greater the likelihood of shared ancestors with shared DNA.

Now, given that there are about 62,000,000 people in the UK today, and each one of us had 128 ancestors at the base of their their trees 7 generations back, and 1,048,576 ancestors 20 generations back, then it doesn't take a genius to work out that the majority of people in the UK will have ancestors shared with lots of other people, because there simply weren't enough people to go around.  And we have not even touched the subject of illegitimacy.  Or the fact that people were mobile, and often travelled hundreds of miles, even when there was no mechanised transport.

David was very lucky to have families in his ancestry which were wealthy enough to leave wills, and a whole branch which lived for generations on an isolated island.  Most of us are not that fortunate.

And, as I also said before, with only 100,000 people out of 7,000,000 in the world actually on the DNA database, that also substantially reduces the chances of ever finding a match.

Incidentally, I have 131 people in my own tree with the surname WOOD, most (but not all) related to my paternal g.g. grandmother.  Maybe we're related ?  Should I take a DNA test ? 

[Nick29]

Your contention about the 128 ancestors floored me a bit as well;  we are dealing with Y-DNA here (this is how we tested), so I take that to mean that if we have a common direct male line ancestor seven generations back - that's what it means.  The female line doesn't come into it at all.  Neither to all the other grandparents.  I will however go back to ftDNA and check this with them.

The problem is that if your g.g.g.g.g. grandfather had seven sons, he would have passed his Y-DNA on to all 7 sons, and not just the one in your direct line.  If each one of the other 6 sons also went on to produce 7 sons over several generations, that's a heck of a lot of people carrying the gene.  How do you find the WOOD from the trees ? (Sorry for the pun - couldn't resist) 

I have a very common surname, and my ancestry hits a wall at about 1805 in London.  I could take a DNA test, but I suspect that it would only lead me back to France, where my surname is the most common name.  DNA testing is great if you want to know the general area where your paternal line originated, but unless you have a name which is very unusual, or linked to a well-documented regal dynasty, it's unlikely to tell you much more.

[Tisy]

Hi Nick,

Correct me if I am wrong, but I think your Wood ancestors are not in your direct male line, as they are connected to your paternal grandmother, so a Y-DNA test would not be appropriate to find a Wood connection.  Y-DNA is only for finding your male line, as the Y-chromosome is passed down from father to son ad infinitum.  This is why my brother had to provide the sample  for our test. You would also not have inherited your X-chromosome from your paternal grandmother, as this is passed down from your mother (and mother's mother etc).  There is the new autosomal test which can determine cousin relationships back five or six generations and this is for both sexes - I am not sure under what circumstances I would use this as I have not looked into it closely;  it may be something to look at if you had groups of people of the same surname with similar DNA.

You might like to try the Y-DNA test to find your haplogroup, which in turn would give you some idea where your male line originated (if as you say it is unusual and possibly French).  This could also give you information on your deep ancestry - for instance if you wanted to participate in the Genographic Project.  Other than that, if you have a good paper trail, and you're not interested in the French connection, why bother?

And yes, you are right;  7x g-grandfather may have had seven sons and we could be descended from any one of them - unless we came up with an exact match (0 genetic distance match) it would be hard to pinpoint.  Of course, the more people test, the more likely it is that we will get a closer match - we will be patient and see what happens.

Tisy

[Redroger]

Yes Nick, It did worry me about my grandfather being 71; however having met definite relatives who descend from his older brother, and noting the similarity between them, and my son, and my brother's sons, I am as sure as I can be without DNA of the line of descent. My tree is difficult enough without what would be a further complication.

[Nick29]

Hi Nick,

Correct me if I am wrong, but I think your Wood ancestors are not in your direct male line, as they are connected to your paternal grandmother, so a Y-DNA test would not be appropriate to find a Wood connection.  Y-DNA is only for finding your male line......

I know that, Tisy - I was being a little sarcastic, hence the 'winking smiley' 

[Nick29]

Yes Nick, It did worry me about my grandfather being 71; however having met definite relatives who descend from his older brother, and noting the similarity between them, and my son, and my brother's sons, I am as sure as I can be without DNA of the line of descent. My tree is difficult enough without what would be a further complication.

It's certainly not impossible, Roger.  I have a deep respect for my own father, who brought up a young family when he was in his 50's (working 2 jobs at the time).  Let's hope your grandfather had some help ! 

[Redroger]

My grandmother killed herself, I think reading the inquest reports it was through undiagnosed post natal depression, so my grand father was left with a 6 year old daughter, and a 2 year old son at the age of 73, and no immediate family within 30 miles. The children were informally adopted (it was 1901) by two of my grandmother's sisters, Dad was brough up on a farm near Wisbech, and his older sister brought up in London, near Euston. They do seem however to have had regular contact.

[marcie dean]

I take it that she was a lot younger than himself probably in her 40's?

marcie

[Tisy]

Hi all,

This is probably a good site for anyone contemplating DNA testing -

http://www.worldfamilies.net/

It provides heaps of good info, which will help anyone to make an informed decision.  The University of Utah site which has already been listed in this conversation was also very good at explaining, in simple terms, how DNA works.

Tisy