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How Good are Matches and Genetic Distance

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  • nathanm
    replied
    Originally posted by Cromdubh View Post
    Thank you.
    I still get a touch of an inferiority complex when corresponding with people who are at ease with statistics.
    Tom Johnson
    Then don't feel that way around me. I'm nowhere near at ease with statistics. On that previous post, I knew his numbers were wrong. It didn't pass the smell test. The likelihood that two events with 1/500 odds both happen together can't have better odds than 1/500. I had to look up the correct calculation myself.

    Leave a comment:


  • ORE
    replied
    Ring translation

    @Cromdubh
    Your post was cut off.... drum roll... the translation was?

    Leave a comment:


  • Cromdubh
    replied
    Spence of Orkney

    Originally posted by ORE View Post
    I recently bought and received my results for a 37 marker test. At 25 markers the test was solidly one surname at 37 it was three surnames with multiple matches. The 25 marker exact matches are documented (they slip to GD of 4 at 37) with a surname closely associated with my own for at least 500 years. My surname is a occupational surname (Spence) and I have not found any other Spence's from Orkney posted here or elsewhere (Ysearch, SMGF, and here).

    I have seen father/son's results posted with a GD of 2 so how do I figure it out what's really the story?

    Has anyone seen drastically different matches from 25 to 37? How about from 37 to 67?

    Does anyone read these posts?
    Oddly enough i met a Spence either from Orkney or descended from Orkney stock at an Irish wedding in Berlin some years back.
    I mention that the wedding was Irish as the estimated drinks bill was fatally flawed.
    This chap could have come from anyplace from the Outer Hebrides to the Southwest of Ireland.
    We even managed to translate the Scots Gaelic inscription on the ring he wore, "Th
    Last edited by Cromdubh; 29 March 2011, 06:11 PM. Reason: Some of the text missing

    Leave a comment:


  • Cromdubh
    replied
    Thank you.
    I still get a touch of an inferiority complex when corresponding with people who are at ease with statistics.
    Tom Johnson

    Leave a comment:


  • nathanm
    replied
    Originally posted by Cromdubh View Post
    How does one "mess" about with Y-search?
    I feel I am looking at a long list of non-responsive data!
    I'm sure that there is a tutorial somewhere, hopefully not pitched as high as the "Binomial calculator" mentioned elsewhere in this thread.
    I never could get my head around statistics.
    Instead of being a useful tool, I found them an unsurmountable roadblock!
    Cheers,
    I think he just meant he was searching for matches on the website. It's not the most intuitive user interface, but as long as you tested through FTDNA, it's easy to transfer your data there. There's a link under "Tools" at the bottom of the menu in the left-hand column, which automagically enters your Y-DNA values into the form on Ysearch. People who tested at other companies have to manually input the values. But that's the primary benefit of using Ysearch besides FTDNA, there are more samples to search for possible matches.

    You don't need to know much statistics to use Ysearch, FTDNA, or most other genetic genealogy websites. I just didn't want a bogus statistical claim to go unchallenged. That's how bad information gets perpetuated. However, it is useful to have some knowledge, because lots of complicated statistics go into the calculations being made.

    Leave a comment:


  • Brunetmj
    replied
    Has anyone ever retested and got new values? Has FTDNA ever tested multiple times on the same DNA to see if the test match each time
    That's a very good question. If I had to guess I would say they don't always between different companies ( testers)

    Leave a comment:


  • Cromdubh
    replied
    Originally posted by EdwardRHill View Post
    I was messing around yesterday at Y-search and I had a close to being a match there. They would have been a match with some of my other matches. But anyway they were from Orkney Islands. So they are people who have a connection to there testing at FTDNA. Sorry can't help with the rest
    How does one "mess" about with Y-search?
    I feel I am looking at a long list of non-responsive data!
    I'm sure that there is a tutorial somewhere, hopefully not pitched as high as the "Binomial calculator" mentioned elsewhere in this thread.
    I never could get my head around statistics.
    Instead of being a useful tool, I found them an unsurmountable roadblock!
    Cheers,

    Leave a comment:


  • ORE
    replied
    RogersDNA Mutation Rates Chart is very good

    Is there any research on what causes the mutation on these locations? Looking at CDY a and CDY b as faster mutating is there certain locations where environmental condition make mutation in markers or certain markers more stable. For example my family have always been snow birds but how about people that like in warmer climates or working with man made chemicals.''

    Would a two step mutations count as less for GD purposes? Are the names related to certain areas on the Y and does any have a good link. I read that a null value which seems a lot more complicated only counts for a GD of 1

    Has anyone ever retested and got new values? Has FTDNA ever tested multiple times on the same DNA to see if the test match each time. I am relatively certain than the overall consistency rate is high. Put my precious daughter was the 1/1000 after my wife had her tubes tied and my first wife died of cancer at 20 to what is usually a slow growing cancer 97% of the time,

    Things are what they are...

    Thanks,

    Leave a comment:


  • nathanm
    replied
    Originally posted by ORE View Post
    The markers that I seem to be off are the CDY a and CDY b. Each by two.

    I also noticed that additional names show up in the projects that do not show up when I show all matches. Do some people only want or allow matches that belong to their project?

    Thanks for your posts.
    Yep, the CDY markers are the fastest mutating ones among those tested. According to this nice looking table, the mutation rate is 0.03531, i.e. about one mutation every 28 generations. (That page doesn't list any references, but the values seem to be taken from this article.)

    As far as matches only showing up for projects, many people have their profiles setup that way. I don't recall whether that was the default or not, but it might not be explained well enough for new testers. Personally, I don't get the point of genealogical DNA testing without trying to find as many matches as possible. Who knows? Maybe you'll match a long-lost cousin who can fill in the blank spots in your family tree.

    Regardless, you can check matches against each project you've joined individually, by going to the Y-DNA matches page and selecting each project in turn under "My Project Groups" at the top of the left-hand menu column.

    Leave a comment:


  • ORE
    replied
    Very Interesting

    The markers that I seem to be off are the CDY a and CDY b. Each by two.

    I also noticed that additional names show up in the projects that do not show up when I show all matches. Do some people only want or allow matches that belong to their project?

    Thanks for your posts.

    Leave a comment:


  • Yaffa
    replied
    Originally posted by ORE View Post
    I recently bought and received my results for a 37 marker test. At 25 markers the test was solidly one surname at 37 it was three surnames with multiple matches. The 25 marker exact matches are documented (they slip to GD of 4 at 37) with a surname closely associated with my own for at least 500 years. My surname is a occupational surname (Spence) and I have not found any other Spence's from Orkney posted here or elsewhere (Ysearch, SMGF, and here).

    I have seen father/son's results posted with a GD of 2 so how do I figure it out what's really the story?

    Has anyone seen drastically different matches from 25 to 37? How about from 37 to 67?

    Does anyone read these posts?
    I dont know if this will help you. I have 2 people DNA tested who are the 2nd great grandchildren of our Patriarch who was born 1813. Both tested 67 marker and are off one mutation from now going back to 1813. Our closest match outside our direct family line is 6 mutations off at 67 marker and they are from Ireland while my ancestor from the US. I have seen lines though related fall apart between 37-67 marker. They are related to us but way back there.


    I also have another line tested 67 marker who is 2 mutations off from a cousin line born in the mid to early 1700's. We are missing paper connecting these two lines though they are related and living in same area.


    Mutations can happen anywhere. Form what I understand some markers may mutate faster than others.

    Leave a comment:


  • nathanm
    replied
    Originally posted by lc0 View Post
    If the mutation rate is (say, but it's not far off) 1/500 then on say 25 markers there is a chance of 1/20*1/20=1/400 of a GD of 2, that is on average 1 out of 400 father/son combinations will show a GD of 2 when taken over 25 markers. That's not all that uncommon
    Your probability calculation is wrong. This problem is an example of a binomial experiment. There are n=25 trials, the probability of a mutation in any given trial is p=1/500=.002, and we're looking for x=2 mutations. A quick Google search turned up this tutorial, with a handy binomial calculator. Plug in those values, and here are the results:

    The probability there will be exactly 2 mutations, p(x=2): 0.001146 or 1/873
    The probability there will be 2 or more mutations, p(x>=2): 0.001163 or 1/860

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  • lc0
    replied
    Re: How Good are Matches and Genetic Distance

    >> I have seen father/son's results posted with a GD of 2 so how do I figure i

    If the mutation rate is (say, but it's not far off) 1/500 then on say 25 markers there is a chance of 1/20*1/20=1/400 of a GD of 2, that is on average 1 out of 400 father/son combinations will show a GD of 2 when taken over 25 markers. That's not all that uncommon

    >> Has anyone seen drastically different matches from 25 to 37? How about from 37 to 67?

    For two knowningly related people in recent time (i.e., anything that makes sense in a genealogical sense like 10's of generations, not 100's: you probably don't care to know that you related to 1000's of people but with a connection >> 1000yrs ago), the expected GD is pretty much 0 for over 30 markers. A GD of 1 for 25 markers means that most likely you are not connected within any reasonable time. Contrary to popular belief, it doesn't matter (much) if the GD is in faster or slower mutating markers, this becomes only of importance when considering 100's of generations, not 10's.

    As you increase the number of markers the expected GD will increase. While it's always worthwhile to check GD of 1 at 37 markers it doesn't become interesting before the GD=0. Of course, there always exceptions, like the father/son with a GD of 2...

    Hope this helps

    Leave a comment:


  • EdwardRHill
    replied
    I was messing around yesterday at Y-search and I had a close to being a match there. They would have been a match with some of my other matches. But anyway they were from Orkney Islands. So they are people who have a connection to there testing at FTDNA. Sorry can't help with the rest

    Leave a comment:


  • ORE
    started a topic How Good are Matches and Genetic Distance

    How Good are Matches and Genetic Distance

    I recently bought and received my results for a 37 marker test. At 25 markers the test was solidly one surname at 37 it was three surnames with multiple matches. The 25 marker exact matches are documented (they slip to GD of 4 at 37) with a surname closely associated with my own for at least 500 years. My surname is a occupational surname (Spence) and I have not found any other Spence's from Orkney posted here or elsewhere (Ysearch, SMGF, and here).

    I have seen father/son's results posted with a GD of 2 so how do I figure it out what's really the story?

    Has anyone seen drastically different matches from 25 to 37? How about from 37 to 67?

    Does anyone read these posts?
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