Haplogroup I Subclades

Subhaplogroups were traditionally distinguished by STR's

Originally posted by GeoffHoward

Regarding Haplogroup I,

Does anyone know why Haplogroup R is most often thought of in terms of its Sub-Haplogroups R1a and R1b, while Haplogroup I is though of primarily in terms of just "I'.

Are I1a, I1b, and I1c the equivalents of R1a and R1b? I would think so, given that they are all identified by SNPs.

Is it that in-depth research came later for I than it did for R?

Hi Geoff,

Its more-or less because in-depth research for I came later - but thats partially because it was hard for researchers to tell them apart using the markers that were traditionally used in the earlier stages of Y-DNA research.

Haplogroups are defined by SNP's which are "unique events" (ie. everyone with a particular SNP is descended from a common ancestor that first developed the SNP, and haplotypes are defined by "microsatellite repeats" (STR's- single tandem repeats), which are "fast mutating" (and thus very useful for looking at small time scale changes in a lineage) but not "unique events" (meaning you can't build up a reliable phylogenetic tree from STR's).

Certain combinations of STR can be correlated with SNP lineages, so for some lineages, eg R. it can be easy to distinguish between the subclades using STR's. Whereas, with other lineages, the STR combinations may overlap slightly (which seems to be quite common in haplogroups like I & J), so its more difficult to reliably predict the lineage when testing SNP's.

I read a great analogy on the rootsweb list a few days ago, by Dennis Garvey.

Imagine sitting out in front of the United Nations building and trying to guess the nationalities of the people you see based just on their clothing.
Often you will be able to draw conclusions based on characteristic dress from some countries. But, of course, the clothing really doesn't determine nationality - it only hints at it. The only way of actually learning their nationality for certain is to check their passports.

That clothing is equivalent to STR haplotypes. Often we see a certain characteristic "style" of haplotype that goes with a certain haplogroup, and are able to make judgement calls based on it. (That's the principle that Whit uses for his haplogroup predictor). But just as with clothing, sometimes what we see is unusual for its group, and we can be misled. We would need to do a SNP test to know the haplogroup for sure (the genetic equivalent of checking passports).

Another analogy that i've thought of recently (i'm not sure yet whether it "needs more polish"), is that the SNP lineages are like branches of a tree, and the STR combinations are like where leaves at the end of the branches are physically located. In some parts of the tree, branches, and leaves do not overlap all that much with other branches & twigs,..but in other parts of the tree, seperate branches of a tree, or seperate twigs of a tree will overlap so that sometimes adjacent leaves (ie haplotypes), are actually from different twigs or branches (eg. different subclades of I, or even between I & J).

Angela.

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