This project welcomes anyone who has been predicted or SNP-tested as Y-Haplogroup T.
Haplogroup T (known as Haplogroup K2 until May 2008) is defined by SNP M184 and is found at low frequencies in the Middle East, Europe and North Africa. Most lines in T belong to subgroup T1a defined by SNP M70 which until March 2011 was considered equivalent to M184.
T1a in turn splits into T1a1 (T-L162), T1a2 (T-L131) and T1a3 (T-L1255).
T1a1 clusters along an east-west axis from Iran to Spain. T1a2 is found both in northern Europe and southern Africa but is rarer in the eastern and western edges of T's distribution zone. To date, T1a3 has only been found in Kuwait.

Recent developments including the Geno 2.0 chip have identified the following major subgroups of T1a:

T-L208 (T1a1a* on the current ISOGG tree http://www.isogg.org/tree/ISOGG_HapgrpT.html)
T-Z709 (T1a1a1*)
T-P77 (T1a1a1a)
T-P322 (T1a2a)
T-L446 (T1a2b)
Most lineages in T will belong to one of these 5 branches. The first two are strictly speaking paragroups and may split into several branches when more data is available.

Thomas Jefferson is believed to have belonged to haplogroup T, based on tests carried out on individuals sharing his paternal line.
For more information on T and the Jefferson family link see:
http://www3.interscience.wiley.com/cgi-bin/abstract/114108057/ABSTRACT
and
http://news.bbc.co.uk/1/hi/sci/tech/6332545.stm