GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2009-12 > 1260124924


From: (John Chandler)
Subject: Re: [DNA] real relatedness or fluff and fairytales?
Date: Sun, 6 Dec 2009 13:42:04 -0500
References: <587770.27617.qm@web24502.mail.ird.yahoo.com><953242.47354.qm@web24503.mail.ird.yahoo.com><91E96C076B6F44FD94D81A3E9CFFB6A3@RESTES2007>
In-Reply-To: <91E96C076B6F44FD94D81A3E9CFFB6A3@RESTES2007>(robertajestes@att.net)


Roberta wrote:
> Since there are two criteria to be fulfilled, both the 7cM and the 700 SNPS,
> I'm presuming that SNPs take up a different amount of space, or there
> wouldn't be two criteria, just one.

That's right. The DNA is not being sequenced here, but rather sampled
at scattered spots. The spacing between the sampled spots is
variable, as you can see if you look at the list of positions of
"successive" SNPs. Looking only at the autosomes, I find, in fact,
156 pairs of successive SNPs that are truly adjacent, but there are
also gaps of as much as 22 million, and the median separation is about
2700. In other words, the amount of space spanned by a fixed number
of SNPs is quite variable.

John Chandler

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