The results of a Y-DNA test are either a string of plusses and minuses, or a series of numbers. The plusses and minuses are the result of a SNP (single-nucleotide polymorphism) test and denote the testeeâ€™s Haplogroup, while the string of numbers are the result of a STR (short tandem repeat) test and denote the testeeâ€™s haplotype.
To learn more oneâ€™s haplotype, or to compare it to otherâ€™s results, most people enter those results into a database such as Ysearch, Ybase, SMGF, YHRD, or the Y-STR Database. To do this, however, it is sometimes necessary to â€˜normalizeâ€™ the numbers. For instance, one testing company might find a result of 27 for DYS481 while another finds a result of 23 on the same individual. This is typically due to different sequencing primers used by each company to characterize each particular STR.
Thanks to a post on the DNA-NEWBIE mailing list (if you are interested in genetic genealogy and not yet a member of this mailing list, you can sign up here), I learned of a spreadsheet that contains conversion numbers for many of the genetic genealogy testing companies:
â€œFor you to be able to derive meaning from your results, you need to compare them to othersâ€™ results. Jim Pearsall, a genetic genealogist who has been tested by several DNA companiesâ€¦compiled the following table of adjustments based on the reports provided to him by the companies.â€
HT: Justin Ryan posted the link to Mr. Pearsallâ€™s conversion document to the DNA-NEWBIE mailing list.