"I got loyalty, got royalty inside my ___" (Kendrick Lamar) (3)
I believe the answer is:
dna
(Other definitions for dna that I've seen before include "Genetic material often used by police" , "Deoxyribonucleic acid (abbreviation)" , "Substance that stores genetic information - often used by police" , "Substance in chromosomes that stores genetic information, used by police" , "Substance in chromosomes that stores genetic data" .)