The focus of the project is on people who are in haplogroup R1b, and additionally have tested DYS464X with a fractional allele (normally 15.3g, with other alleles being some combination of 14c, 15c, 16c, 17c, and/or 18c). You do not have to test before joining; you will simply be put in the "untested" grouping until you have results avavailable. People who do not meet the project criteria and wish to join because they are interested in tracking results are also welcome. People who belong to haplogroup R1b or one of its subclades are also encouraged to join Tibor Fehér's R1b and Subclades project.

When the small number of results with fractional alleles were first noticed at SMGF, the question was raised as to whether the fractional allele was unique enough, and stable enough, to serve as a "mini-SNP" distinguishing a cluster of families. It is not. Currently there are four known R1b clusters that feature a fractional allele.

• Reynolds-Cooper cluster, DF5+, 15.3g, and "cccg"
• Secher cluster, L21+, 14.3c,  and "cccc"
• Murphy cluster, L159.2+, 15.3g, and "cccg"
• Hadley cluster, L2+, 15.3g, and "cccg" [predicted]