OK, a result came in for one of my projects that has a null marker. I understand what they are, and that they are rare, but how rare? I tried to find something about the frequency with which they occur, but didn't find anything. Next, the statement from FTDNA regarding the null marker is: "A value "0" for any marker indicates that the lab reported a null value or no result for this marker. All cases of this nature are retested multiple times by the lab to confirm their accuracy. Mutations causing null values are infrequent, but are passed on to offspring just like other mutations, so related male lineages such as a father and son would **likely** share any null values." The emphasis on the word "likely" is mine. Does that mean that a null marker can mutate back to a number between generations? Or does it mean that for some reason the null marker in this case was not actually a mutation? Say grandfather has a value of 12, son has a null marker, could the grandson have a 12? Rick Saunders