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STR's related to time

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  • STR's related to time

    Suppose two related people with the same surname match, say, 36 out of 37 markers and you want to determine who exhibits the original allele and who has the subsequent change. Is there any tendency in the way the STR's change? i.e. do they:

    a. tend to increase in no. of repeats over time?
    b. tend to decrease in no. of repeats over time?
    c. there is no clear tendency, they can do either.

    Thanks for your insights.

    -Rob

  • #2
    Don't hold me to this, but here's my semi-educated guess. The first question would be which marker is the difference on. Then, what is the haplogroup. Also, what geographic area the paternal line is from might have some bearing.

    I would think that in certain haplogroups, certain markers have a tendency to go in a certain direction, upward or downward. This can be seen, for instance, in haplogroup R1b. The modal value for DYS390 is 24. However, it seems that more mutations off that value are 23 than 25. So for that haplogroup and that marker, it's more likely to go down. I'm sure there are other examples for other haplogroups.

    I don't think this is something inherent in the biology of that marker. It probably has more to do with chance mutation in someone whose descendants are very numerous. In the case above, the original man who mutated from DYS390=24 to 23 had many descendants, much more than someone who had the mutation to 25. DYS390=23 in an R1b is one of the indicators of what's called "Frisian" R1b, because it seems to be found a lot in northern Netherlands (Frisia) and northern Germany. In turn, Frisian R1b haplotypes are considered to have a good chance of testing S21+. S21 defines the R1b1c9 subclade. One estimate is that 20% of R1b1c men would test S21+.

    Plus, you can't look at one marker in isolation. Frisian R1b tends to have DYS390=23 and DYS447=24 (both off the R1b modal) in combination. So you would want to establish what geographic type you're looking at and consider the mutational difference between the two men in that light.

    Do you have a specific example or is this just a general question? If it's a specific example, tell us the details and we may be able to tell you more.

    Mike Maddi

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    • #3
      Originally posted by MMaddi
      Do you have a specific example or is this just a general question? If it's a specific example, tell us the details and we may be able to tell you more.

      Mike Maddi
      Thanks for your thoughtful response.

      It's a bit of both actually. In my specific case it is the difference between a 15 and 16 at DYS 458. If I read Nordvedt correctly, 15 seems to be the modal value for my haplogroup, (I1a), so perhaps 15 was the earlier value and a repeat was later added?

      In the larger picture I could imagine that an understanding of which markers tended to go which way over time would be especially useful in large surname projects.

      -Rob

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      • #4
        I've looked at Ken's webpage where he posts various types of I haplogroup haplotypes. He does a good job of showing the key markers for each type by highlighting them in yellow.

        If you go to his new website at http://knordtvedt.home.bresnan.net/ and click on the link for IModalI.xls, it'll give you an Excel spreadsheet which shows you the various types in the I haplgroup and which are the key markers.

        Looking at that spreadsheet, he has 20 or so different types of I1a. Only 4 of those have 16 as the modal for 458. (One has 14 as the modal.) All the rest of his I1a types have 15 for the modal.

        Have you established which of his I1a types you're likely to be? In his scheme, these seem to be key markers for distinguishing the various types of I1a - 385a-b, 390, 446, 447 and 449. There are others that may be helpful too in your case.

        First of all compare your full haplotype to his various I1a types and see if you can determine which you are closest to. Then look at the 458 value for that type and see if it's 15 or 16. That will probably, not definitely, tell you what's the ancestral value for 458 in your specific paternal line.

        If you don't have Excel to view the spreadsheet, but your haplotype is on ysearch, tell me the ysearch ID and I'll see if I can come up with more information from his spreadsheet.

        Mike

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        • #5
          Originally posted by MMaddi
          .... compare your full haplotype to his various I1a types and see if you can determine which you are closest to.
          Mike
          Many thanks for your insights!

          I have sat and looked at Ken's spreadsheet for hours, but nothing seems conclusive to my bleary, untrained eyes. Right out of the gate I have 15,15 at 385a,b, which doesn't even appear in any of Nordvedt's I1a modal haplotypes. My ysearch is WDNFB if you or others wish to take a look.

          -Rob

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