DNA and the Book of Mormon

For the sake of diplomacy, I try not to disparage the beliefs of other denominations, but it's always a little confusing to me when fundamental Christians attack the Book of Mormon on the grounds that, so far, no DNA evidence has been traced back to Lehi's party.

The reason it confuses me is that these are the same people who deny genetic evidence of evolution.

As long as the discussion is on the LDS church, genetics is rock hard science which cannot be denied or ignored, but when the topic turns to evolution, genetics suddenly becomes this mystical, devilish pseudo-science which is not to be trusted.

I don't mean to make any generalizations about any particular denomination, but there are simply some individuals who need to make up their minds.

Is genetic science reliable, in which case, evidence against the Book of Mormon is inconclusive, but evolution is true and their belief is deeply mistaken?

Or is genetic science unreliable, in which case evidence against the Book of Mormon is inconclusive and their argument falls apart anyway?