A Canadian thoroughbred, Northern Dancer's offspring earned more money and won more major stakes races than those of any other sire up until the 1990s.
He sired 147 stakes winners including the great Triple Crown winner Nijinksy II, as well as The Minstrel, Shareef Dancer, Secreto, Northenette, El Grand Senor, Lomond and Fanfreluche, among others.
Coolmore founder John Magnier and legendary trainer Vincent O'Brien were responsible for bringing the Northern Dancer line to Ireland and the Coolmore empire was founded on his progeny.
The speed gene was first identified by Dr Hill in 2010 and she co-founded Equinome, a UCD spin-out company, which has developed the Equinome Speed Gene Test.
The test is used by the global bloodstock and racing industry to identify the optimum racing distance for individual Thoroughbred horses, allowing racehorse owners and trainers to choose race distances which will suit their horses.
"Having first identified the speed gene in 2010, we decided to see if we could trace the origin of the gene variant using population genetics coupled with pedigree analysis," says Dr Hill. "We wanted to understand where speed in the Thoroughbred came from."
To find out, the team analysed the speed gene type in almost 600 horses. These included 22 Eurasian and North American horse breeds, museum bone and tooth specimens from 12 Thoroughbred stallions, 330 elite-performing modern Thoroughbreds from three continents, 40 donkeys and two zebras.
Dr Mim Bower, from the University of Cambridge, says their findings point to a British mare as the most likely single founder of the original speed gene.
Their research found that the prize stallions of the 17th and 18th centuries had two copies of the T-type speed gene variant (T:T), which is linked to greater stamina.
At that time, races were held between two horses, competed over multiple heats, at distances of between two to four miles, and repeated until a horse had won the event twice or 'distanced' the opponent. Horses did not race until they were five or six years old, and then only two or three times in their lives.
"This is consistent with these horses being T:T types," says Dr Bower.
Later, the focus of racing switched to faster horses that developed earlier and two- year-old races became popular during the last century, a preference that continues today.
The scientific findings show just how influential breeding trends are on the genetic make-up of the racing horse population.
"For example, in Australia, the myostatin speed gene type (C:C), which is best suited to fast, short-distance sprint races, is more common and there is a market driven demand for horses with at least one copy of the C-type gene variant," says Dr Hill.
To identify where the C-type gene variant originated, the researchers analysed DNA samples from more than 20 breeds.
Those sampled included local British and Irish horses, from where female Thoroughbred lineages derive, and exotic eastern populations, from where male Thoroughbred lineages originate.
The scientists identified the Shetland breed as having the highest frequency of the C-type gene variant. While Shetland ponies are worlds apart from today's racing thoroughbreds, they represent local British horse types, which were the most common racing horses before the Thoroughbred was formally founded.
"The results show that the speed gene entered the Thoroughbred from a single founder, which was most likely a British mare about 300 years ago," concludes Dr Hill.