AncestryDNA has just rolled out enhancements to their Clustering Program that let you “Create custom clusters”. At AncestryDNA > DNA > Matches > By Clusters/Pro > Create custom clusters. You must have the additional subscription for ProTools to access this program.  I have not run it through its paces yet, but I wanted to review the Walk The Clusters Back (WTCB) concept, and ask for feedback on your experience with it.

The concept of WTCB is to adjust the cM range to focus on two generations at a time. The idea is to “solve” the Clusters for close relatives and then adjust the range down to include Matches in the next generation back, and then see where the Clusters separate into more distant Clusters. Start easy with a range of 90-400cM which is the recommendation for the LEEDS method to determine four groups. This would be roughly four Clusters with each one focused on a separate grandparent. Tag (by Dots or by Notes) every Match to the appropriate grandparent. Then drop the range to, say, 70-200cM to get mostly Clusters that include Matches who are 1C on a grandparent, and 2C on a Great grandparent. I don’t know of anyone who has found a “sweet-spot” range for each generation, and I suspect it might be different for each of us. The last time I did this WTCB I had to “fiddle” with the ranges – and never could find any range that gave me only Clusters with Matches from only two generations in each Cluster. So, get used to that.

The point is to notice when some Matches you’ve tagged to an Ancestor, then show up in different Clusters based on a new range – and then determine which sides are represented by the new clusters. Then tag all of those new Matches appropriately.  Example: you have a Cluster with 20 Matches that is focused on a Great grandparent.  Tag all the Matches with that grandparent (if not already tagged as a closer Ancestor). Adjust the range to add more Matches. Look in the new Clusters for the previously Tagged Matches – hopefully there are two new Clusters, but maybe three. From my experience there may be two Clusters with 15 to 25 Matches, each of which include some of the 20 Matches from the previous run. These new Clusters would represent the next generation back and the focus would only be one of the two parents of the previous Cluster.

Yes, it gets harder and harder with each new generation. The good news is that a Cluster with known Matches from one generation, can only morph into Clusters going back from that one Ancestor. This reduces the genealogy effort . If you’ve reviewed all of your ThurLines (and used ProTools to add even more Matches), you have likely tagged a lot of Matches out to 6C. So as the 4C and 5C and 6C Clusters start to form (as you reduce the cM range), you may already see the Ancestor for the new Clusters by looking at the Notes.

Use your judgment, and fiddle with the cM ranges. Please report back on your experience, and/or if you find a sweet spot for some range. Note that the sweet spot should include two generations – the one you’ve figured out and the next one you are working on.

[19P] Segment-ology: Walk The Clusters Back at AncestryDNA by Jim Bartlett 20251017