Board Thread:Theories and Speculation/@comment-29769110-20161017201027/@comment-734582-20171009200738

Natrix Spiritual Cloak Gleam wrote: It could be a plot twist, since the dna test matched which is clear proof, karin could simply be lying for sarada's sake. Yea no. That's not how DNA tests work. I mean when it first came out we couldn't be sure if it was intentional, but considering the reveal in the end of Gaiden that it was indeed Sarada's own cord, it's clear it was.

If you match your own DNA, then it's a 100% match. A parent-child DNA match would be around 50%. Suigetsu assumed that the cord was Karin's (IE between karin and her mother), but it's really between Sarada and Sakura (again, why it's 100%, since it contains Sarada's own cells).