Genetic testing is an important step in linking your genealogy back to a known ancestor when you have reached the end of the written records available or to confirm the validity of traditional genealogical research. In surname tracing such as the Nixon DNA Project, the Y Chromosome is used as the starting point to provide this genealogical link. In order to fully understand your results from FTDNA, you may wish to read some articles on population genetics and molecular evolution. There are some free discussions of this available on FTDNA and other websites (as well as a number of textbooks if you are keenly interested):

https://www.familytreedna.com/understanding-dna.aspx

https://en.wikipedia.org/wiki/Y_chromosome

The short version:  FTDNA tests small areas (genetic loci or loci,singular locus) of the Y Chromosome known as Short Triplet Repeats(STRs). Scientific study has documented that STRs change more rapidly than other regions of the Y Chromosome, but the exact rates of change are still being investigated. However, good estimates for many of the commonly examined loci exist and can be used to determine the calculated number of generations (genetic distance) between two individuals. A table of the mutation rates on these loci is located here:

https://en.wikipedia.org/wiki/List_of_Y-STR_markers

The number which most concerns genealogical researchers is the statistical mutation rate. This rate varies between STRs and can quickly tell you how closely you are to other members of the Nixon families.  The following 12 markers are analyzed by the basic 12 marker package available from FTDNA (calculated mutation rates are included in ()):

DYS393/DYS395(0.00076)

DYS390(0.00311)

DYS394/DYS19 (0.00151)

DYS391(0.00265)

DYS385(0.00225)

DYS426(0.00009)

DYS388(0.00022)

DYS439(0.00477)

DYS389i(0.00186)

DYS392(0.00052)

DYS389ii(0.00242)

So,what does this tell us about our Y Chromosome relatives? Take for instance the very slowly changing DYS426 with a mutation rate of 0.00009. This locus is observed to change about 9 times in every 100,000 transmission events. Therefore, if you and another Nixon differ at the DYS426 locus, you are about 10,000 generations apart. Since the chance for the locus to change occurs every time the Y Chromosome is passed from father to son, tracing the genetic path of the Y Chromosome up to your most recent ancestor and then back down cuts the genetic time in half. In our hypothetical example, the most recent ancestor would be about 5,000 generations back. Since average human generational time is considered to be between 22 and 32 years,this would place the two individuals separated by a DYS426 locus at about 110,000 (5,000 x 22 years) if they had a common ancestor. 

The NIXON Y-DNA Project seeks to use these known rates of mutation to group participating Nixons into related family groups and assist with tracing ancestry.