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Archiver > DNA-R1B1C7 > 2007-08 > 1186005864


From: "David Wilson" <>
Subject: Re: [DNA-R1B1C7] Modal value for CDY (WAS: Confusingclassifications)
Date: Wed, 1 Aug 2007 15:04:24 -0700


Yes, that's basically correct--modal haplotypes can change subtly depending
upon the size of the population from which they are calculated.

Note that CDY is a fast mutator. That means that over time you will end up
with a relatively flat distribution curve for allele values for this marker,
which further means that the count for the values found at the center of the
curve can be similar. For example, when I did my first modal haplotype
calculation a couple of years ago, I had 20 haplotypes in which CDYa = 38,
and 23 in which CDYa = 37. On those statistics, the mode for CDYa was 37,
but the victory was close.

In the current R1b1c7 project data set, we have 65 haplotypes with the value
37 for CDYa and 90 with the value 38. So based on the larger sample set, the
modal value is 38. The difference is larger here, perhaps because we have a
disproportionate number of project members from the Doherty/Daugherty/etc.
project, and those haplotypes tend to have the higher value. But even
without the Doherty effect, it seems to me that 38 is the better number
because of the larger sample set.

This issue has come up before in the context of the larger R1b1c haplogroup.
There the modal value for CDYa wobbles between 36 and 37 depending on the
sample set. There was another marker, too. DSY456? Can't recall right now.
These wobblers might go away if we calculate modal values only for specific
subclades of R1b1c rather than lumping them all together.

I generally disregard CDYa and b for haplogroup analysis because they are so
volatile. I think they definitely have a potential role to play in close-in
analysis within family groups.

David W.



On 8/1/2007 8:16:08 AM, thomas and catherine tucker
() wrote:
> On August 1st David Wilson noted recent reasons on FTDNA
> R1b1c7's
> projection:
>
> I know this seems inconsistent in a big-picture view, but it is probably
> consistent with the FTDNA projection algorithm, whose details are
> proprietary and which is undoubtedly fairly complex.
> >
> [Original Message]
> > From: David Wilson <>
> > To: <>
> > Date: 8/1/2007 10:30:43 AM
> > Subject: Re: [DNA-R1B1C7] Confusing classifications
> >
> David my question is about a clarity on CDY a? In the Niall marker modal
> and also on the Northwest marker modal displayed on your written tablet of
> "The Northwest Irish Variety" modal ... CDY a ... is 37. However, in the
> colorazation chart CDY a at 37 is considered a miss for the modal.
>
> Was there a shift in value because more R1b1c7's
> (SNP deep clade tested)
> have a consistently different read on that marker...therefore, the
> standard
> value changed?
>
> Thank you,
>
> Thomas Tucker
>
>
>
> I know this seems inconsistent in a big-picture view, but it is probably
> > consistent with the FTDNA projection algorithm, whose details are
> > proprietary and w

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