Since March 2012, Y-DNA results in the Welsh Patronymic Project have been grouped at two different levels.

1. Haplogroup and Subclade.

The major grouping is by Haplogroup, and Subclade within haplogroup. People in different haplogroups or subclades cannot be closely related. Men in different major groups are unlikely to have a most recent common ancestor (MRCA) within the last 10,000 years (for major haplogroups) or within 5,000 years or so for subclades within a haplogroup.

If you share a haplogroup or subclade with a person of interest, it is likely that your Most Recent Common Ancestor (MRCA) lived within the last 5,000 years or so.

Results for testers for whom we have not yet found a match, or have too few markers tested to allow reliable matching, will be placed in one of the Unassigned groups.

Haplogroups are determined by a small number of mutations on the Y chromosome, known as Single Nucleotide Polymorphisms (SNPs), or Unique Event Polymorphisms (UEPs). Haplogroups in green have been confirmed by SNP testing. Haplogroups in red have been predicted by Family Tree DNA based on the individual's STR results and can be confirmed by a Deep Clade SNP test.

2. Closely related group.

To share an MRCA within recorded history, FTDNA calculates that you need a match within the following degrees of genetic distance (GD), i.e. the number of marker mismatches:

12 markers tested: 0,1

25 markers tested: 0, 1, 2

37 markers tested: 0, 1, 2, 3, 4

67 markers tested: 0, 1, 2, 3, 4, 5, 6, 7

The closer the match, the closer the relationship is likely to be – more or less! This is only a rough guide, and other information should be factored into the match wherever possible.

“Within recorded history” is a very loose term. For Wales, this would be since about 1100AD.