Josie,

That's a keen observation and a good question about the
number of differences in our mtDNA in relation to the CRS
reference.

Let's start by saying that the CRS (Cambridge Reference
Sequence) is just an arbitrary reference selected by some team of geneticist
that were among the first to study the genetic sequences of mitochondrial
DNA.  They decided to use the sequence of one of their subjects as a
comparison reference, maybe one of their own samples, who knows?.  The
selected mtDNA belongs to haplogroup H, the most prevalent haplogroup in
Europe.  Therefore many European persons who get tested have few
differences if any with the CRS reference.

Next, what the commercial
tests show us about our mtDNA is not the whole sequence of mtDNA but just one or
two regions:  HVR1 and HVR2 (Hyper Variable Regions).  Supposedly
these two regions don't have any medical implications so having a fewer more or
a fewer less mutations is not very sign