The world's first equine clone will challenge naturally bred runners next month in Nevada.
Idaho Gem was the first clone born from a horse family
Idaho Gem is a mule created three years ago by cloning DNA taken from a foetus produced by the parents of a champion racer.
It will race against another mule clone and a full field of non-clones.
The two clones have been separated for two years, so their performances could offer insight into the role of the environment in development.
The University of Idaho scientists who cloned Idaho Gem also produced two other cloned mules in 2002 from the same DNA.
One of those two, Idaho Star, will compete against Idaho Gem along with naturally-bred mules in Winnemucca, Nevada, and on the California racing circuit this summer.
Analysing how the clones perform against each other will give scientists information on how variables like diet and training regimes affect developing racing mules.
Those behind the race say that just because they carry the DNA of past champions, there is no guarantee the clones will be successful.
Nature vs nurture
"We know they have the genetic capability to be great," said Don Jacklin, president of the American Mule Racing Association, who leases Idaho Gem from the University of Idaho for about $1,000 (£533) a year.
"We don't know if they are going to have... the attitude to want to run and want to compete and want to win."
Mules are produced by breeding a female horse with a male donkey and are usually infertile.
Gordon Woods, the lead scientist on the University of Idaho project that created the clones was keen to emphasise there was nothing abnormal about the cloned mules.
Idaho Gem (r) will race against Idaho Star (l)
Dr Woods told the Associated Press that the mule cloning project also provided insights into human cancer research and, in particular, calcium's possible role in tumour development.
Trainers have been putting the two clones through their paces at a track in Stockton, California.
Mr Jacklin said he hoped cloning technology would eventually be embraced by the horse racing industry as another breeding tool.
But The Jockey Club, thoroughbred racing's governing body in North America, keeps an extremely tight rein on breeding practices.
Only natural breeding methods are allowed, and club rules explicitly prohibit not only cloning but artificial insemination of any kind.
In the UK, cloning is banned in horse racing but could be used in competitions such as show jumping.