With no X-DNA inherited from some ancestors, varying amounts of X-DNA inherited from others, the randomness of DNA recombination at each generation, and occasional segments passed down intact over several generations, X-DNA can be quite unpredictable and it can be difficult to identify exactly where it came from.

It is common to share segments of X-DNA with people who share no significant amount of autosomal DNA.

Males generally get far fewer X-matches than females.

X-DNA’s best and most practical use is for isolating matches to particular family lines, even though the amount inherited cannot tell you from whom or how far back it came.

Nor can the absence of any X-DNA disprove your relationship (except for immediate family members – see below).

Focus on larger X-matches, such as 20cM or more, as smaller segments may not be reliable (or may just be too far back).

For X-matches on FTDNA’s Family Finder, use the chromosome browser to check the segment sizes, as FTDNA includes very small segments (down to 1cM) in their total cMs, and you want to exclude those tiny segments and only count segments of 7cM or more.