A lot of traits in humans and animals are complex. With this, we mean that those traits are genetic but aren’t inherited by a simple recessive or dominant model. All these traits are a total sum of tens or even thousands of genetic variants. These are called polymorphisms instead of mutations because each variant occurs a lot on its own in the population.
Complex traits are being influenced by many genetic variants, which is why the presence of these polymorphisms don’t give an indication of the horse’s genetic potential on their own. Besides that, differences between individuals for a complex trait is being influenced by both multiple genetic factors and environmental factors.
Performance is also a complex trait, but we can say something about the genetic background of it. For horses, they have for example discovered the “speed gene”. The presence of this polymorphism is of influence for the speed of thoroughbred horses in races. Besides that, there is a gene that people call the “gate-keeper”, which is partly the reason why a horse can perform certain routines.
Sequence polymorphism in MSTN predicts sprinting ability and racing stamina in thoroughbred horses; Emmeline W. Hill, Jingjing Gu, Suzanne S. Eivers, Rita G. Fonseca, Beatrice A. McGivney, Preethi Govindarajan, Nick Orr, Lisa M. Katz, David MacHugh; PLoS ONE 2010. Mutations in DMRT3 affect locomotion in horses and spinal circuit function in mice; Lisa S. Andersson, Martin Larhammar, Fatima Memic, Hanna Wootz, Doreen Schwochow, Carl-Johan Rubin, Kalicharan Patra, Thorvaldur Arnason, Lisbeth Wellbring, Göran Hjälm, Freyja Imsland, Jessica L. Petersen, Molly E. McCue, James R. Mickelson, Gus Cothran, Nadav Ahituv, Lars Roepstorff, Sofia Mikko, Anna Vallstedt, Gabriella Lindgren, Leif Andersson & Klas Kullander; Nature 2012.