I is a Haplogroup subclade ....
How to get from “Adam” to the I branch in the Haplogroup tree is not covered here. ISOGG has been restructuring the ISOGG |main tree in 2016 after it laid dormant for a few years. So even identifying the path to I is in flux after being stable for a number of years. This is true with the other tree services such as yfull as well.
We do introduce here the major branching below I. This so any ancient (greater than 5,000 years ago) discussion is covered here and not on a Family Branch or yDNA Groupings page for that Family line.
As of May 2016, using the YCC longhand nomenclature, I is simply identified as I. Most prefer to use either I1 or I2 though which specify the next of two major branches after I. The shorthand form for these two next level branches in I are I-M253 and I-M438; respectively. I itself is officially I-M170.
So far, there is only a single Family line in Haplogroup I, and they are deep below I1. The ISOGG tree is behind on expanding the branching further for I leaf nodes. The farthest down the Haplogroup tree path for the family group in this project in the ISOGG tree as of May 2016 is I-L338. The path to I-L338 from I is:
Most are starting to use the YCC shorthand form to identify each branch point; and then even the path to it. The new form is to simply list a single, main SNP or allele to identify each branch point. This way, the branch designation for unaffected areas do not change when whole sections are moved around and restructured.
I 1 - a 2 a insert 1 a 1 a 1 YCC Long Form in ISOGG
M170 > M253 > DF29 > Z58 > Z59 > CTS8647 > Z60 > Z140 > Z2535 > YSC261 > L338 YCC Short Form in yFull
Each branch point often has many SNPs identified with it; sometimes ten to thirty. We usually list the FamilyTreeDNA SNP used to name a branch here.