Sonia...I definitely understand your confusion since I'm confused as well. But, I think for someone to take the time to develop this app, there must something important attached to it. I'm still wondering if it is similar to mutations in STR testing. My uncle has a null or 0 at str 425. Apparently this is very rare and there is actually a null 425 group project at FTDNA. I do know that along with having a 0 at 425 if you match on most of the other markers and belong to the same haplogroup, there is a definite connection between the those who have this mutation.