What genes are made of (3)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
dna
(Other definitions for dna that I've seen before include "Genetic-code molecule" , "Substance in chromosomes that stores genetic information, used by police" , "Substance in chromosomes that stores genetic data" , "Substance that stores genetic information in body" , "Substance that stores genetic information - often used by police" .)