Hi Mike,
It's nice to hear from another descendant of the
Aberdeenshire area. My mother's ancestors (MILNE) hail from
Aberdeenshire as well. Specifically from Aboyne and Cruden,
Easter Gask, and Glentanner.
Because Legacy has recently expanded its capability in
recording DNA results I am going to take that as an
opportunity to temporarily stretch the definition of the
purpose of the LUG under the guise of helping us better use
Legacy. That stretch is based on the need to understand not
only what is being recorded, but the meaning and implication
of the DNA data. Without that understanding we might easily
impart meanings, and draw conclusions about our lines that
are incorrect, and therefore lead others astray. It is not
my intent to open lengthy discussion of DNA testing, other
than about how such testing impacts our use of Legacy.
Mike, you posed two questions:
1. Is there some way we can determine at what point in time
these trees converge, and at what accuracy?
2. Is {/Are/} there areas where the DNA matching is simply
not true?
Addressing your second question first, DNA testing is very
accurate, and assuming there was no contamination of the DNA
samples, or errors in the handling and testing of those
samples, you can consider the DNA matching to be "true."
The testing results are what they are. It is in the
interpretation of those results that some questions arise.
Addressing your first question, when attempting to determine
the distance back in generations to a Most Recent Common
Ancestor (MRCA), it is important to remember that the
numbers provided by any DNA testing firm are _only an
estimate_ of the number of generations back to an MRCA.
The various research labs, and the genetic testing community
have established how often genes may be expected to mutate,
making it possible to base relational estimates on a
combination of the number of markers tested, and the number
of markers matching between any two Y-DNA samples.
The firm with which I contracted to test my Y-DNA was
FamilyTreeDNA (FTDNA). FTDNA bases their estimates on
mutation rate studies conducted by the University of Arizona
and offers Y-DNA tests for 12, 37 or 67 markers. Estimates
of the distance between two samples is provided as a
percentage probability that the MRCA was no further back
than a certain number of generations.
For example, for a 67-marker test, if all 67 markers match
between two samples, then it is estimated that there is a
50% probability that the MRCA was no further back than 2
generations. If only 66 of 67 markers match, that sets the
estimate of a 50% probability back to 4 generations. The
percentage of probability increases as you push back further
in generations. That is there is a 90% probability for a
MRCA at 4 generations for a 67/67 match, and a 95%
probability for a MRCA at 6 generations for an 67/67 match.
In other words, as the number of markers tested decreases,
and the number of matches, decreases, the estimate to
generational separation from an MRCA increases.
You do not say which firm tested your samples, or how many
markers in the 46-marker test, were matched between the
tested samples. The testing firm should be able to provide
you with an explanation of their test results. That
explanation should include their rationale for their
estimates of generational separation.
I hope this helps, and did not stray too far from the
intended purpose of the Legacy User Group
John Zimmerman
Mesa, AZ
On 7/17/2011 10:56 PM, Mike Bridgeford wrote:
> Hi John,
> You seem to be quite knowledgeable about DNA interpretation. I must say I
> have really battled to comprehend the significance of the various results.
> We have a unique family name, Bridgeford/Bridgefoord, which through research
> has been centred around the Aberdeenshire areas of Scotland.
> We have several Bridgeford family trees which we can't link up, as
> documentation is no longer available from the early days in Scotland.
> In four of these trees, we have managed to find male descendants, and have
> had their DNA Y-chromosome tested, in a 46 marker test. The results are that
> two are related at MRCA 10 and MRCA 14 to my DNA markers. The third person is
> not related [here we presume that there is an illegitimacy somewhere and the
> name is carried through by the female link, and hence no DNA Y-chromosome
> match].
>
> Is there some way we can determine at what point in time these trees
> converge, and at what accuracy. I believe that the MRCA 10 , for example,
> indicates that the convergence was 10 generation age. Is this correct? And
> what variance can be expected in terms of generations?
>
> The other thing that really puzzles me, is that when viewing results from
> Ancestry.com, for example, there are many people with MCRA values of 3 or 4,
> and no apparent surname association. After intensive investigation from both
> sides, there is no apparent link at all. It seems almost impossible to
> believe that our forefathers sired that many illegitimate children on
> overseas visits!!!
>
> Is there areas where the DNA matching is simply not true?
>
> I would be most appreciative if you would be able to answer some of my
> questions, or perhaps put me in contact with someone who can.
>
> Very Confused,
>
> Mike Bridgeford
> Plettenberg Bay
> South Africa
>
>
>
> -----Original Message-----
> From: hwedhlor [mailto:[email protected]]
> Sent: 17 July 2011 07:10 PM
> To: [email protected]
> Subject: Re: [LegacyUG] DNA entry
>
> Richard,
>
> MtDNA is not reported as a complete set. Each DNA testing
> company has different defined marker sets, but they all
> compare those sets to the Cambridge Reference Sequence
> (CRS), then report deviations from that sequence, not the
> entire list, which would include 569 values (bases) for
> HyperVariable Region 1 (HVR-1) and another 574 values for
> HVR-2 (Note that some testing companies define a 3rd HVR
> region, taking some values from the HVR-2 region and placing
> them in that third area). Personally I'm not at all
> interested in entering 1143 values. Instead I entered only
> "CRS" in the HVR-1 column for myself, as my HVR-1 values did
> not differ at all from the CRS values. In HVR-2 I entered
> only my five values that differed from the CRS. Allowing
> for 20 deviations from the CRS in each of the three
> recognized regions seems sufficient. I can't speak for the
> rest of the Legacy user base, but I think it doubtful any of
> them would vary from the CRS by anything close to 20 values
> in each of the three HVR columns.
>
> As for the values for each entry field, typically an mtDNA
> value is a 4-digit entry. That is three digits for the base
> location, plus a letter signifying the specific component
> (adenine, guanine, cytosine or thymine, represented by A, G,
> C or T). For example, if the CRS at location 195 is T, and
> the person being tested has a component at 195 of C, then
> the deviation would be reported as "195C". It is possible
> to have additional values (insertions) at a given location.
> In that case they would be reported using the base location
> (for example "195C") with the addition of a decimal and a
> number. For example "195.1C". Two insertions would be
> reported as 195.1C and 195.2T. Deletions (missing base
> location values) are also possible. In such cases the
> missing location is reported as a number followed by a minus
> sign. For example "195-". Using those notational standards
> it is highly unlikely that any give value would exceed 7
> digits, so 10 is more than adequate.
>
> Regards,
>
> John Zimmerman
> Mesa, AZ
>
> On 7/17/2011 7:46 AM, Richard Van Wasshnova wrote:
>> You can't input your complete mtDNA in v.7.5.0.98 anyway.
>> The template only goes up to 20 entries (of 10 letters) in each HVR.
>> We'll all have to wait for the next update.
>>
>
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>
>
>
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Archived messages after Nov. 21 2009:
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