Surprised this hasn't been brought up yet...

[sekrah]

https://www.bloodhorse.com/horse-racing/articles/246372/penn-vet-researchers-develop-test-to-detect-gene-doping

[Boscar Obarra]

How early does this stuff have to be administered in a horses growth cycle to have an effect ?

[belmont3]

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