Archiver > GENEALOGY-DNA > 2010-11 > 1291068365

From: Kathy Johnston <>
Subject: Re: [DNA] Provenance of a DNA segment (importance ofphasedhaplotypes)
Date: Mon, 29 Nov 2010 17:06:05 -0500

> Did Walsh give any derivation for
> his 1 in 10,000,000 statistic?

In case I misread the information, let me quote exactly what was said in the lecture:
“A random one cM block being called a match is < 5%.
The odds of a run of 5 cM is 1/10,000,000.
The odds of a run of 10 cM is 1 X 10 to the -14.”

> Has anyone observed that many short
> segments in a Family Finder match? My
> matches show an average of 10 segments,
> with a range of 5 to 18.

Maybe Bruce said ~ 50 "shared" segments not necessarily small segments. First cousins could have this many segments in common but I would expect longer ones. He could also have said 15 and I wrote down 50. Who knows? I don’t hear as well nor can I write as fast as I used to. I was trying to get an idea of the algorithm being used but I still don’t quite get it when it comes to the significance of the smaller segments. Does anybody remember?

Bennett Greenspan uses the small segments for visually lining up sequences on the chromosome browser to determine pedigree lines. Maybe that is the main reason for showing the sequences down to 1 cM.

Kathy J.

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