It carries genetic information (3)
I believe the answer is:
dna
'it carries genetic information' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for dna that I've seen before include "Genetic material often used by police" , "Substance that stores genetic information - often used by police" , "Deoxyribonucleic acid (abbreviation)" , "Substance in chromosomes that stores genetic information, used by police" , "Briefly, substance in chromosomes used by police to identify criminals" .)