https://www.bloodhorse.com/horse-racing/articles/246372/penn-vet-researchers-develop-test-to-detect-gene-doping
How early does this stuff have to be administered in a horses growth cycle to have an effect ?
Interesting story.
PCR Polymerase Chain Reaction is also used in Covid testing
Off topic I suppose but the inventor of PCR was Kary Mullis who wrote an interesting book:
https://www.amazon.com/Dancing-Naked-Mind-Field-Mullis/dp/0679774009
Highly recommended for the curious