Wonky DNA test? (spoilers)

Martens gets the call about the DNA test... "it's not you, your test is negative... but the other sample is 99.9%! Now just tell me you know whose it is!"

Wouldn't it have to be obvious to anyone who looked at both sets of DNA that the two samples came from a father & son pair?
Doesn't half of each parent's DNA make it to the child? Of course those genes get shuffled a bit, but I always thought the relation would be pretty blatant.