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FTDNA STR Testing and Methodology

Family Tree DNA ("FTDNA") has posted comprehensive and helpful FAQs concerning Y-DNA STR testing
 
The FAQs explain
how genetic distance translates into closeness of relationship at different testing levels. They also explore how genetic distance translates into closeness of relationship for matches with the same surname – an event that, given the relatively late adoption of and fluidity of surnames in much of the Ashkenazi Jewish population, occurs far less often for Ashkenazi Jews than for members of many other groups.

The FAQs also
explain that FTDNA on December 12, 2012 changed the manner in which it calculates genetic distance (i.e., number of steps) for: (1) some palindromic markers (i.e., some of the markers reported with more than one number); and (2) null values. As a result, some matches are now reported as being closer than they once were (and as closer than would be calculated using the Y-Utility).

Joseph Robert Goren        Rabbi, by Joseph Robert Goren
Joseph Robert Goren (1916-2012)        Rabbi, painted by Joseph Robert Goren