Ydna markers are STRs (Short Tandem Repeats). So for example at location say 522 there is GATTAGATTAGATTAGATTAGATTA would be shown as DYS522=5. So a number lower means the sequence was cut off when copied and a higher number means an extra number of the sequence was copied. Note: none of the DNA companies report partial sequences.
That is something I didn't understand...thank you for explaining. Am I right in understanding that the mutation can go both ways...that the sequence could be copied with only four repeats instead of five or vice-versa so one can never tell which one is the original?