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Archiver > GENEALOGY-DNA > 2006-08 > 1154563043


From: "Daniel Jenkins" <>
Subject: RE: [DNA] research strategy for genealogists
Date: Wed, 2 Aug 2006 23:57:23 +0000


Ann,

Thanks so very much for anwering my basic question so clearly.

Dan Jenkins




----------------------------------------
> From:
> Date: Wed, 2 Aug 2006 11:40:21 -0400
> Subject: Re: [DNA] research strategy for genealogists
> To:
>
> In a message dated 8/2/2006 3:23:57 AM Pacific Daylight Time,
> writes:
>
> >
> > Ann and Diana,
> >
> > Since you both are far more expert than I regarding the significance of the
> > markers,could you look at the
> > markers I posted yesterday and offer me an opinion. Do these particular
> > markers put weight in any direction of possible relationship. I now find that
> > there are 2 people who have the same surname that
> > are a one step mismatch at 4 markers with the gentleman I am helping.
> > Unfortunately one has not posted his results to Y-Search
> > so I am unable to get a handle on his line or know if he is related to the
> > other with same surname. My gentleman has no knowledge of his line prior to a
> > gr. grandfather born 1846 and only a guess as to the fathers' name, and
> > only a first name for the mother. I looked at the MRCA comparison at FTDNA and
> > appears 25-28 generations seems reasonable . This would be after naming
> > period .
> > If the 2 matching surnames are not related , would this lend credence to a
> > possible adoption or non paternal event in my gentlemans' line. I would tend
> > to assume the 2 matching surnames are likely related
> > somewhere way back.I have exhausted all usual resources on finding the
> > origins of the unamed father of the child born 1846. I may be grasping at straws,
> > but that seems
> > to be all I have at moment. I can give you more details off list if you want
> > to look at what I have to date.
> >
> > Dan Jenkins
>
> You raised several points in this and your prior message.
>
> 1) Do the particular markers that differ put any weight on the relationship?
>
> No, the effect of fast versus slow markers is quite trivial compared to the
> absolute number of mutations, and it is the opposite of what intuition might
> tell us. If two people differ on fast markers, their common ancestor is slightly
> more distant than if they differ on slow markers.
>
> 2) Is a 33/37 match with people of different surnames, but whose ancestry
> goes back to the same vicinity & timeframe, worth pursuing?
>
> Not in my view. The reason is that allowing so many mismatches widens the
> pool of candidates enormously. There are 74 different ways to differ by one step
> (one more or one less repeat at each marker). There are 2,738 ways to differ
> by two steps: each of those 74 haplotypes could differ in 74 different ways,
> but half of those would revert back to the original
>
> 74*74/2 = 2,738
>
> Doug McDonald posted the general formula for J mismatches in N markers in his
> response to my post (scroll down in my post to get his URL):
>
> http://archiver.rootsweb.com/th/read/GENEALOGY-DNA/2004-09/1095511528
>
> It's (2*N)^J/J! (2 times N raised to the Jth power divided by J factorial)
>
> For a 33/37 match, that's
>
> (2*37)^4/4! = 74^4/(4*3*2*1) = 1,249,441 distinct ways of differing by 4
> markers on a 37 marker test.
>
> 3) Is the MRCA calculation from FTDNA grounds for optimisim?
>
> Not in my view. They use a higher mutation rate for FTDNATip reports than
> found in the current literature for father/son pairs. If you multiply their
> numbers by two, that is more in line with direct father/son studies. Their
> qualitative guidelines are sensible, but keep in mind they apply to people with the
> SAME surname.
>
> http://www.familytreedna.com/GDRules_37.html
>
> It's interesting to note that their figure for a common ancestor for a
> perfect 37-marker match (50% chance within five generations) is more in alignment
> with father/son mutation rates from the literature. Their FAQ
> http://www.familytreedna.com/faq2.html gives 2-3 generations for a perfect match.
>
> MRCA calculators are based purely on the behavior of random events, with no
> further knowledge. If we took a very large pool of people who matched 37/37,
> 50% would find their common ancestor within five generations, and 50% would have
> to keep on looking. People with the same surname (a piece of "prior
> knowledge") are more likely to be somewhat bunched in the first 50%.
>
> Ann Turner
>
>
>
> ==============================
> Census images 1901, 1891, 1881 and 1871, plus so much more.
> Ancestry.com's United Kingdom & Ireland Collection. Learn more: http://www.ancestry.com/s13968/rd.ashx
>

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