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Archiver > GENEALOGY-DNA > 2014-01 > 1390054498


From: Ann Turner <>
Subject: Re: [DNA] cM v. SNPs
Date: Sat, 18 Jan 2014 06:14:58 -0800
References: <008c01cf1432$56e9b1b0$04bd1510$@oneotaslopes.org>
In-Reply-To: <008c01cf1432$56e9b1b0$04bd1510$@oneotaslopes.org>


Yes, it sounds like you're looking at segments from your maternal and
paternal side.

I suspect rounding the HIRs to the nearest million bases accounts for the
difference. SNPs are not uniformly distributed, so the actual segments
could be offset a little bit and have different cM / SNP counts. Below are
instructions from Tim Janzen on how to get the "exact" segment boundaries.
I put "exact" in quotes because the boundaries are still a little bit
fuzzy, but they're where the first contradiction occurs (opposite
homozygotes).

Ann Turner


=====

1. Log onto your 23andMe account using Firefox as your browser.
2. Go to the Family Inheritance feature at
https://www.23andme.com/you/inheritance and then go to "Genome View".
3. In the Firefox menu bar click on "Tools", then click on "Web
Developer", then click on "Web Console".
4. Right click anywhere in the console. This should bring up a menu
that has 3 options in it. Click on "Log request and response bodies".
5. Select the two people you want to compare using the dropdown menus
in Family Inheritance and wait for the matching segment information to
appear.
6. Go to the Web Console and scroll down to the very bottom of the
console where you should see a line that is the 2nd row from the bottom that
reads: "POST https://www.23andme.com/you/ibdview/" as well as an HTTP
extension after that. Click on this line.
7. This brings up a box that says "Inspect Network Request". Scroll
down to the very bottom of the box to the "Response Body" section. In this
section you will see a subsection called "intervals". This subsection
contains the start and stop positions for each matching segment and is
organized by chromosome.
8. Copy the start and stop positions for each matching segment into
another spreadsheet so that you can save it.

=====



On Sat, Jan 18, 2014 at 1:39 AM, Eric S Johnson <>wrote:

> Two people are 23andMe matches on my dad. Here are the HIRs per FI:A:
>
>
>
> PersonA: ch8:11-15mbps, 8.8 cM, 1494
>
> PersonB: ch8:11-15mbps, 8.6 cM, 1531
>
>
>
> (Neither are in Dad’s AF CSV download, so I can’t get more-precise start
> and stop points, can I?) Assuming their matches on Dad are IBD (not a sure
> thing, of course), the fact that they don’t match each other (in FI:A) can
> be explained by their HIRs being opposite halves, right?
>
>
>
> But how can an HIR which is longer in cM be less SNPs?
>
>
>
> Best,
>
> Eric
>
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