GENEALOGY-DNA-L Archives

From:
Subject: Re: [DNA] How many STRs??
Date: Sun, 4 Apr 2004 03:30:42 EDT

I may be alone in this, but my concern is in trying to get a better handle on
the probabilities between the "minimal" TMRCA and the maximum. If this has
been addressed in any detail on this list, I either missed it or I didn't
realize it!

Example (using Dr. Walsh/'s calculations):

"slow" mutation model [chosen because my two samples with 12 transmission
events have 0 mutations, we don't have the 37 marker results yet,but for
illustrative purposes let us assume 37/37]

12/12 match has P[MRCA<=14]= .50 P[MRCA <=53]=.9 P[MRCA<= 71] =.95
P[MRCA>=72]= .05
25/25 match has P[MRCA<=7] = .5 P[MRCA<=24] = .9 P[MRCA<=32] =.95
P[MRCA>=33]=.05
37/37 match has P[MRCA<=5] = .5 P[MRCA<=16]=.9 P[MRCA<=21]=.95
P[MRCA>=22]=.05
It appears a 43 marker match would be represented by P[MRCA<=4]=.5, but what
is the effect of a 43/43 on the 5 - 26 generations probabilities? Especially
if you add in reality that there is NO MRCA within the five most recent
generations, i.e. P[0<=MRCA<=5] = 0. Therefore, P[MRCA<=7] - P[0<=MRCA<=5] =
P[<=6MRCA<=7] = .5 - 0 = .5.


<-------------------------------------------------------.5/.5-----------------
------------------------------------------------->
<----------------------.5<----------------------------------------------------
-------------------------------.4|---.1-------->
<---------------.5<---------------------------------------------.4|<----------
------------.05|.05------------------------->
|-Reality-----0|<.5---|<-------------------------------------.4|<-------------
---------.05|.05------------------------->


|--1--2--3--4--5--6--7--8--9--10--11--12--13--14--15--16--17--18--19--20--21--
22--23--24--25--26--|

Now, in my particular situation, the genealogical paper trail pretty well
makes P[MRCA=6] = 1.0. However, I have a related line of 2 samples that match
each other 25/25 and match MY line at 24/25 and the P[0<=MRCA<=6] = 0 (unless
you want to fantasize some kind of bigamy situation with families in two
different states at the same time LOL). The two lines have a 12/12 match, and a
24-1-0 match. The one mismatch is "fast" moving marker. Again, let us assume, for
illustrative purposes, a 36/37 match between the two lines.

Q. Does the "slow" mutation model still hold for the 12/12 match? I would
think so.

<-------------------------------------------------------.5/.5-----------------
-------------------------------------------------->
<----------------------------.5|<---------------------------------------------
----------------.4|---.05--------------->|.05->
<-----------------.5|<---------------------------------.4|<---------.05|.05---
---------------------------------------------->
|-Reality--------0|<------.5|<----------------------.4|<---------.05|.05------
------------------------------------------->


|--1--2--3--4--5--6--7--8--9--10--11--12--13--14--15--16--17--18--19--20--21--
22--23--24--25--26--|

What additional refinement to these probabilities would a 43 marker test add?
These are the questions I have about adding more markers.

Anne W. Nelson

In a message dated 4/3/2004 10:43:53 AM Central Standard Time,
writes:
In a message dated 03/28/04 9:05:45 PM Pacific Standard Time,
writes:

Does anyone out there know how many STR loci exist in an average
Y-chromosome? Of course, we'll have to define an STR loci, for example a
site on the Y-chromosome where about 3 nucleotides are repeated at least 6
times.
Mark Jobling's paper "The Human Y Chromosome: an Evolutionary Marker
Comes of Age" . <snip>
http://www.le.ac.uk/genetics/maj4/JoblingTS.03.NRG.Review.pdf

The published sequence can be searched with a computer program for STRs
(Short Tandem Repeats, also called microsatellites). There are ~ 100-200
"potentially useful" new microsatellites. The actual utility depends on
studying them in various populations to see if they vary and if they have a useful
mutation
rate.

> Are the majority of people upgrading from 25 to 37 really gaining much
> benefit, or have most already got about all they need to know at 25?

It's too soon to tell, as very few people have reported their results, but
there is the law of "diminishing returns." Going from 12 to 25 shows a
dramatic
difference in narrowing the time frame for the Most Recent Common Ancestor;
going from 25 to 37 doesn't help as much.

http://dnaheritage.com/markers.asp

Ann Turner - GENEALOGY-DNA List Administrator
Search or Browse the archives, Subscribe or Unsubscribe at
http://lists.rootsweb.com/index/other/Miscellaneous/GENEALOGY-DNA.html

This thread:

• Re: [DNA] How many STRs?? by

  • Re: [DNA] How many STRs?? by
  • Re: [DNA] How many STRs?? by