TOKYO, July 29 (Reuters) - Tokyo"s athletics programme will see the inaugural 400 metre mixed relay event kick off on Friday, where teams of two men and two women will compete for Olympic gold against each other offering fans unpredictable and intriguing match-ups. The United States will be the favourites for Saturday"s final, assuming there are no baton blunders in Friday"s heats, having claimed the 2019 World Championships in Doha. Jamaica are also expected to feature prominently. But there is a level of unpredictability to the race, since there are no gender rules governing the order in which athletes race. In the Doha world title race, for instance, Poland went for men in the first two legs and women in the last two while the rest of the teams ran the first and fourth legs with men. The move gave Poland a sizeable lead after the second leg, but they saw that cut back in the third before losing it completely in the fourth as the American Michael Cherry took a lead he never relinquished, helping his team set a world record time of 3.09.34 minutes. Jamaica came second and Poland eventually finished fifth. The unpredictability of how teams choose to run their athletes promises to keep fans guessing throughout the event, though the man-woman-woman-man running order is favoured by most teams. Germany boast this year"s world-leading time after they posted a 3:13.57 minute performance in June at home, according to World Athletics data, followed by Ukraine and Nigeria. Kevin Borlee, Belgium"s 2011 World Championship 400 metre bronze medallist, told Olympics.com that the event has expanded the potential pool of countries that can offer genuine competition in Olympics relay racing. "With the traditional relays you need at least four athletes of the same gender," he said earlier this year.