It's the symbol.
Look for the symbol.
It has BEEN THE KEY ALL ALONG.
(Aside from the DNA sequence link? It's half of an infinity sign. If I am not mistaken, it shows up in three scenes where we see "two sides of a coin" in personality -- Niki-Jessica, Hiro-olderHiro, and Peter-Sylar.)
More coherent analysis later when I can QUIT FLAILING and making SQUEAKING noises about how much I love this show.