Autosomal DNA is shuffled up and becomes diluted with each new generation. The following figures show the average amount of autosomal DNA shared with close relatives:
50% mother, father and siblings
25% grandfathers, grandmothers, aunts, uncles, half-siblings
12.5% first cousins
6.25% first cousins once removed
3.125% second cousins, first cousins twice removed
0.78% third cousins
0.20% fourth cousins
The percentages can vary. A son might for instance inherit 53% of his DNA from his mother, but only 47% from his father. While the Family Finder test is sensitive enough to detect shared DNA for most third cousins, some fourth cousins will test and not have a match. It is recommended wherever possible to test the oldest generations in your family to maximise your chances of finding matches with your more distant cousins. Rather than test myself I have therefore had tests done on my mother and father as part of the beta-testing programme. My dad's results have now come through. My mum unfortunately sent off the vials without including the brushes and is having to redo her test so it will be a while before I get her results! When the results came in I was very surprised to discover that my dad had 12 matches despite the fact that the test is still very new and there can be no more than a few thousand people in the database at present. One of his matches is in the second to fourth cousin range. The remaining matches are what FTDNA terms "speculative" and are in the fourth/fifth to distant cousin range. The screenshot below shows how the matches are presented with the names of the matches obscured for privacy. You will need to click on the picture to enlarge it to see the details.
The speculative matches at the fifth to distant cousin level will in most situations not be worth pursuing because of the difficulties in researching every line back this far. I have already done a substantial amount of research on my father's line but it was quite sobering when I looked at his pedigree to see how far back I could trace all the branches. Although I can trace some lines back to the 1600s, and in some cases back to the 1200s, I have been less successful with my research in some of the other lines. I can currently identify fourteen of my dad's sixteen great-great grandparents, but just eight of his thirty-two great-great-great grandparents. In most instances I've taken the line back beyond the censuses to a specific parish, but a substantial amount of parish register reconstruction in many different counties would now be required to trace these lines further back in time. I also have a substantial brick wall with a certain William Hunter who was born c.1798 in Scotland. He married in 1828 in Stepney and appears in both the 1851 and 1861 censuses in Limehouse in the East End of London where he rather unhelpfully tells us that he was born in Scotland with no indication as to the county or parish. There are rather a lot of William Hunters born around this time on the Scotland's People website and it would be a huge undertaking to trace and eliminate each one. I suspect that because of the large number of Scottish emigrants to America William Hunter will be responsible for the majority of my dad's matches with cousins on the other side of the Atlantic.
There are further Family Finder features in development. The test will eventually give percentages based on ethnic origin, though this feature would probably not tell me very much as I anticipate that I would be 100% European on both my maternal and paternal lines. More interestingly, I understand that results will eventually be reported for the X-chromosome, and there are plans for a separate X-chromosome browser. The X-chromosome has a special inheritance pattern which makes it easier to pinpoint the ancestor contributing the shared X-chromosome so this should be a very useful tool.
The Family Finder test is not a replacement for Y-DNA and mtDNA testing, but it can be a useful complement to those tests, and can be particularly useful for proving relationships in the last four generations. As with all DNA testing it is a tool which needs to be used in conjunction with the paper records. Its value will grow as the database becomes larger and there is more chance of finding meaningful matches. I've seen a lot of orders going through my FTDNA projects, and I'm sure that it will not take long for that to happen.
© Debbie Kennett 2010
18 comments:
Debbie,
Thanks for the review of the Family Finder test. I'm anxiously awaiting my dad's results. Will test my mom at a later date.
Thank you Mavis and Andrew for your kind comments. It's a very exciting new test, and it will be interesting to share some of the success stories.
I have received my results - and had several matches. 2 at the 4th cousin level, although we have yet to find the connection. I did have a cousin contact me who matched at the 5th to distant cousin level and I found 6 ways that he and I are connected! I've also been blogging about it in case you are interested: http://nancycrivers.com/blog/
Thanks Nancy. You've done an interesting write-up and you did well to locate the possible match in the paper trail.
I had my dad's DNA tested through FTDNA right before he died at age 90, 2-1/2 years ago. He was an only child and so am I, so I was hopeful of finding connections to his line through DNA. So far I haven't found any. Do I understand correctly that if I wanted to have his DNA tested for the family finder I would need another sample, which is of course impossible?
Hi Nona,
FTDNA keep all the DNA samples for 25 years so they should be able to do a new test on your dad's sample if that's what you want. Get in touch with them and explain the situation. I'm sure they'll be able to help.
Excellent review all stistics are dead on.
Each child always gets 50% of their autosomal DNA from Mom and the other 50% from dad.
a given grandparent, however, may not contribute the round 25% of their grandchild's autosomal DNA because of the phenomenon of crossing over. That is why the predicted relationship will become less precise with each generation of separation.
Still this review nails how exciting the program is and the statistics are inordinately accurate!
Benjamin
The exciting thing about these new tests is that if you test close family relations you can actually see for yourself the percentages of shared DNA. Children do not always inherit exactly 50% of their DNA from each parent. Tim Janzen has compiled a spreadsheet with results from known relations who have tested which you can find here:
http://kquilting.homeserver.com/23andme/ref.html
As you can see, the percentages vary from about 47% to 53%. These data are derived from the 23andMe test which is very similar to FTDNA'S Family Finder test. 23andMe customers tend to take the test mostly for medical reasons, and it is less useful for finding genealogical matches as a lot of the matches aren't interested in genealogy and don't want to correspond.
Regarding the apparent 47/53 split... Isn't it more likely that this represents the inevitable inaccuracies of the methodology, rather than requiring an exotic uneven split of parental DNA ?
The methodology is correct, but autosomal DNA is inherited on a random basis. The 47/53 split I quoted is perhaps an exaggeration, but there can sometimes be small differences. There are some statistics on this ISOGG wiki page which you might find of interest:
http://www.isogg.org/wiki/Autosomal_DNA_statistics
A son receives an X chromosome from his mother and a Y chromosome from his father. In terms of size, the X is much bigger than the Y. The X is about 3% of the genome, which is why some companies will report that a son shares 53% of DNA with his mother and 47% with his father. This is due to the X chromosome and not because, for example, a child inherited two copies of "Gene A" from his mother and none from his father (that never happens). A child gets one complement of chromosomes from each parent, but for a son, the mother's X means that she contributes more physical DNA than the father. 23andme members can look at this thread for more info about DNA statistics -- https://www.23andme.com/you/community/thread/5936/ :)
Many thanks Andrea for the interesting link. It's fascinating to see the variations in the percentages between different relations.
I'd like to know what the ancestry percentages mean. I am told I am 92 percent Western European and 8 percent Middle Eastern with Palestinian, Jewish, Mozabite, Bedouin and Druze, in that order. Did the Neolithic migrations of middle easterners to Europe have a lasting effect on the autosomal gene pool or is this necessarily more recent? All of my UK and French lines have been in North America for 11-12 generations.
Don't read too much into your Population Finder results. It does not mean that you have ancestors from the Middle East. These are simply your closest matches from the reference populations. There are no British reference populations in the database other than Orcadians (people from the Orkney Islands). My dad also came out with a small percentage matching the Middle East. All his lines have been in England for hundreds of years. You can read more in the Population Finder FAQs here:
http://www.familytreedna.com/faq/answers.aspx?id=22
The tests will eventually provide more meaningful information. The People of the British Isles Project has found marked regional differences in the British population:
http://www.peopleofthebritishisles.org/
Preliminary results were presented by Professor Sir Walter Bodmer at a conference in Cardiff recently. It should eventually be possible to give percentages of ancestry from say Devon and Cornwall. The south-east of England is more homogenous. Bodmer also found a clear divide between North and South Wales.
Hi Debbie,
Nick again. In your last response to GKS you say all your father's ancestors have been in England for hundreds of years, but in your original post you say that you can only find 8 of his 32 3X Greats. Depending on how old he is I would suspect is 3X greats were born between say 1780 and 1820.
This leaves a huge possibility for finding non-English (even those possible Mid-Eastern indications) in the ancestry of his other 24 3x greats.
As far as the Orcadian population goes, I've read mixed messages on whether this is generic Orkney or a mixed UK group. Here is what researcher Prof. Doug McDonald said about it 3 May 2011:
"when FTDNA started their PF, the only academic
samples from the British Isles were Orkney (from the HGDP)and Ireland
(from a medical study, but available from Illumina).
However, very recently a good set of real English became available.
The result of using English instead of Orkney is that quite
a bit more people test as 100% English instead of say 90% English
and 10% something more eastern or southern."
Nick
Nick,
In the 1700s there was minimal immigration into England. The chances of someone from the Middle East turning up in a sleepy English village at this time and marrying a local English girl must be virtually nil!
I understand that the Orkney samples are indeed from Orkney and are not a mishmash. In the People of the British Isles study they even found distinct variations within the Orkney Islands. The English samples that are now available in the Human Genome Project are from the People of the British Isles Project. The researchers had the whole genomes sequenced of about 100 people in the project, but I don't think they provided the detailed geographical information which would make the results more meaningful. FTDNA do not appear to have added this new reference sample to their database as far as I'm aware.
Debbie,
It doesn't have to be limited to someone arriving from the Middle East in the 1700s. It could be 1600s or 1500s or even before.
Look at Benjamin Disraeli and his predecessors. Sephardic Jews who ultimately trace back to Middle East roots who arrived in England circa 1748. Do you think none of the descendants of this family ever married into English families? These connection will and do show up in the DNA.
The Romani (Gypsy) people are ultimately from South Asia (India and surrounds). We know for a fact that they were in Scotland and England quite early and that they certainly, at times, intermarried with Anglo Saxon and other "historically" English people. This will show up in the DNA of descendants to some extent.
I don't know if we ultimately agree, or are working at cross purposes. I just think one needs to take a long view with these DNA results and not limit oneself to thinking that a small Middle Eastern influence in your DNA results is wrong.
Nick
I agree that traces of exotic DNA could potentially turn up in people of British ancestry but I just don't think there are sufficient data yet to draw such inferences. It would be a different matter if there were a sizeable reference population from the British Isles on which the percentages were based. I know a lot of people with British ancestry who are getting these small matching amounts with Middle Eastern populations. This is simply a symptom of the lack of adequate reference samples. It doesn't mean that large sections of the British population have Sephardic Jewish ancestry. You shouldn't read the results too literally. Population Finder is in any case still in beta-testing.
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