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Archiver > GENEALOGY-DNA > 2003-11 > 1068425220


From: Fred Vines <>
Subject: Re: [DNA] Measurement of fragment lengths
Date: Mon, 10 Nov 2003 11:47:00 +1100
References: <LPBBIOAJJFIEMAHJCAPAAEEDDGAA.maldodd@sapo.pt>


Malcolm I wish I hadn't read this, you have now made me doubt my simplistic understanding of what this DNA for
genealogy is all about. Even re-reading Nancy Custers excellent Contexo website is starting to convince me that I
need a little more than the uneducated grey matter I'm stuck with. I have been cruising along thinking that the
test results are integer numbers of the replicates at each marker position. If the tests determine a number to 2
decimals what is this measuring? How do fragment lengths become involved in counting the number of replicates? Why
would FTDNA feel the need to round off such results if it causes us to then see a mutation, for a difference of
0.02? Nancy, HELP!
Fred Vines


----- Original Message -----
From: "Malcolm Dodd" <>
To: <>
Sent: Sunday, November 09, 2003 11:53 PM
Subject: [DNA] Measurement of fragment lengths


> Others with more technical expertise will be able to comment on a perceived
> problem.
> When two cousins have DNA STR markers which are measured at say
> Male A 11.46
> Male B 11.44
> the group administrator would be unaware of this information as it would
> probably be reported as
> Male A 11.46 = 11.5 = 12
> Male B 11.44 = 11.4 = 11
> a one-step difference.
> Non-experts such as myself tend to treat the results from the laboratories
> as "gospel truth" but it is not necessarily that simple and we may well make
> assumptions about the genetic distance and MRCA on a false assumption.
> Malcolm
>
> ______________________________



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