"It's in my ___" ("I was made for this") (3)
I believe the answer is:
dna
(Other definitions for dna that I've seen before include "Bodily substance that stores genetic information - police use it to identify" , "Substance in chromosomes that stores genetic information, used by police" , "Genetic profile" , "Genetic code" , "Briefly, substance in chromosomes used by police to identify criminals" .)