In elite athletics, good genes are useful for more than just competition and training. As noted by Nick Harris of the Daily Mail, genes are also useful when it comes to avoiding testing positive for PEDs:
The most common type of drug test globally analyses urine to compare levels of testosterone (T) and another hormone, epitestosterone (E) to give a T/E ratio. This test can signify the use of all kinds of illegal drugs, including anabolic agents, which are the most commonly found drugs in dopers, 50 per cent of positive drug tests being for steroids — or artificial testosterone.
When the T/E ratio exceeds four to one, it signifies possible doping. But people who have the ‘doping with impunity’ gene variant — carriers have two copies of a particular version of a gene called UGT2B17 — do not return positive tests, even if they have been doping.
The gene variant keeps the T/E level low, naturally. That means huge swathes of the population have a licence to dope.
Despite what the IOC would like you to believe, the testing that Olympic athletes undergo is far from a guarantee that they remain drug free. After all, how effective can it be when up to 81% of a population is naturally predisposed to testing negative on the most common drug test? So much for an even playing field.
The article goes into more detail, so click the link to read more.