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From: "Ken Nordtvedt" <>
Subject: [DNA] What is a clade?
Date: Tue, 14 Oct 2008 08:13:58 -0600


I don't think a too-formalistic definition of "clade" in the context of dna-based population studies or genetic genealogy is needed. The dictionary definition is something like: a clade is the collection of descendants from a common ancestor.

By what means and to what degree of certitude the descendency of the clade members from their common ancestor is established varies. But if the preponderance of evidence leads to the common descent from a founder, then the clade concept seems useful to me for organizing human haplotype data and learning things about population histories.

"Haplogroup" has been enlisted as the name for a clade identified by its members sharing some up-til-now basically unique mutational states, most often ydna or mtdna SNP mutations. This is rather straightforward. Clades can also be identified when member haplotypes show several unique STR repeat values which the probabilities show most likely indicate descent from a relatively recent common ancestral haplotype. This necessarily involves probability assessment, can be subject to error with insufficient discipline (especially with regard to individual haplotype membership on the "fringe" rather than existence of the clade as such), and makes some nervous for establishment of a clade.

Ken


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