The genetic "alphabet soup" is made up of four chemicals known as nucleotides. A SNP (Single Nucleotide Polymorphism) occurs when a nucleotide (one of four molecules—adenine, cytosine, guanine, or thymine) mutates to one of the others. For example, A > T. For the Y chromosome, new mutations (if any) are present in the male at conception and passed on to all patrilineal descendants (the male line), many of whom aquire new mutations and pass them down through their own male lines, adding additional degrees of discoverable uniqness to each line. By testing distantly-related males, the origins (places and dates) for the SNPs they have in common can be estimated, which can then be placed on a timeline, as below. New SNPs are regularly discovered and the timeline is shifted and reordered based on the new data. The timeline below approximates the relatedness between the Cooleys and the Hacketts based on two testers.

SNPs are named only when they move from private (unshared) to shared status. Until Don Cooley tested, those in the pink box were known to belong only to the Hackett tester. Once they were matched, they were given names. As other testers are found to have some of the same SNPs, the list will again be re-sorted and in regards to the timeline. Just like a genealogical tree, the SNP tree will expand and become more precise with new data, which will eventually suggest a likely bithplace, perhaps even family, for John Cooley.

EKA stands for Earliest Known Ancestor. TMRCA is the The Most Recent Common Ancestor.