It's what makes you you (3)

I believe the answer is:

dna

(Other definitions for dna that I've seen before include "Substance that stores genetic information - often used by police" , "Substance that stores genetic information in body" , "Double-helix molecule (abbr.)" , "Genetic-code molecule" , "Bodily substance that stores genetic information - police use it to identify" .)

I've seen this clue in The New York Times.

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