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From: "Ken Nordtvedt" <>
Subject: [DNA] SNPs, Clades, and Trees
Date: Sun, 6 Sep 2009 10:38:55 -0600


A recent message sent by someone to a large mailing did not give a fully on-target rendition of my perspective on the relationships between clades, SNPs, and the y tree. I wrote the message below to clarify and thought this perspective might be of interest to others.


Here's what I found over the last 4 1/2 years in the hobby. It is that extended haplotypes of many STR markers can be used to discover clades (present day populations which descended from distinct founders), especially clades whose ancestry branched away from the rest of the Y tree sufficiently early (probably prior to the advent of agriculture and more rapid population growth). Most of the clades I found in haplogroup-I (now numbering in the several dozens) had then no SNP to define or tag them. And many still do not have SNP tags. SNP tags are not necessary to have a clade or to find a clade. In the early days of the hobby there was hardly any interest by the testing companies to look for more SNPs for hobbyists to use to trace their deepest ancestry. Pressure from the hobbyists, and willingness to pay well for SNP information, was one of the key factors which drove the companies more recently to get more involved in SNPs. The hobby today is different from what it was in January 2004.

SNPs have the ability to tell the temporal order of the nodes in the tree (Node A is upstream of Node B, etc.), something which is often difficult to do with the STRs. SNPs will become increasingly important as the y tree details are pushed toward the present.

And finally; even with the much more numerous SNPs known today by a variety of means, the known SNPs still are a tiny drop in the bucket of all existing SNPs on the y chromosome. It requires further technology developments to bring down the costs so we can all obtain our full set of SNPs since genetic Adam --- a number which is approximately 2000, but bundled into as few as 50 or so phylogenetic packages. A new y SNP occurs on average in every y line about every father/son generational transition.

But contemplate this: our grandsons one day will be able to recite, if interested, their unique ancestral line back to genetic Adam by giving the choices their line took at each of the 50 or so nodes it passed through in that journey. Ken


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