Skip to main content
« Back to the lexicon overview

Predictive height test (HMGA2 Pony)

Height in animals depends on various factors (e.g. genes, environment and their combination). A genetic variation has been discovered for the height of ponies. A base pair change in the HMGA2 gene can influence/reduce height. This is especially influential in Shetland ponies and related breeds.

In Shetland ponies, this test allows breeders to estimate the height of offspring. Here, the ponies are assigned to three height groups: A/A (Small: ~ 84 cm), A/G (Medium Small: ~ 98 cm) and G/G (Normal: ~ 104 cm). 

Although predicting specific heights in other breeds is not possible, the test is also appropriate for other pony and miniature horse breeds to predict if they will be on the smaller or larger size within the breed.

General Information

  • Height in animals depends on multiple factors including genes and the environment.
  • Variants in 4 genes have been shown to account for 83% of height in horses.
  • One genetic variant (a single basepair change in the HMGA2 gene) has a strong influence on height in ponies and miniature horses.
  • This test enables breeders to predict a Shetland pony’s approximate adult height before it is fully grown and to plan breedings to select for taller or shorter ponies.
  • These heights are not applicable to other horse breeds, but ponies with the respective genotypes are smaller than others in the same population. Most horse breeds have the G/G (“normal”) genotype.
  • In larger horses, other genetic variants (not all of which have been identified) have a greater impact on height. In Warmbloods, for example, a variant in the LCORL regulatory region influences height. See the Height test – Horse for further information.

Test Information

This test detects the change of a single basepair in exon 1 of the HMGA2 gene.

Genotype and Lab Report

A/A = “Small”: Shetland ponies will reach an average height of 84 cm.

→ Depending on mating, offspring will be either “medium small (G/A)” or “small (A/A)”.


G/A = “Medium small”: Shetland ponies will reach an average height of 98 cm.

→ Depending on mating, all three genotypes and heights are possible (G/G, G/A, A/A) in the offspring.


G/G = “Normal”: Shetland ponies will reach an average height of 104 cm.

→ Depending on mating, offpring will be either “normal (G/G)” or “medium small (G/A)”.


These specific heights are not applicable to other breeds, but the variants will still have some impact on the height of a pony or miniature horse.


Frischknecht, M., Jagannathan, V., Plattet, P., Neuditschko, M., Signer-Hasler, H., Bachmann, I., Pacholewska, A., Drögemüller, C., Dietschi, E., Flury, C., Rieder, S., Leeb, T.: A Non-Synonymous HMGA2 Variant Decreases Height in Shetland Ponies and Other Small Horses. PLoS One 10:e0140749, 2015. Pubmed reference: 26474182. DOI: 10.1371/journal.pone.0140749.


Makvandi-Nejad, S., Hoffman, G.E., Allen, J.J., Chu, E., Gu, E., Chandler, A.M., Loredo, A.I., Bellone, R.R., Mezey, J.G., Brooks, S.A., Sutter, N.B.: Four loci explain 83% of size variation in the horse. PLoS One 7:e39929, 2012. Pubmed reference: 22808074. DOI: 10.1371/journal.pone.0039929.


Signer-Hasler, H., Flury, C., Haase, B., Burger, D., Simianer, H., Leeb, T., Rieder, S.: A genome-wide association study reveals loci influencing height and other conformation traits in horses. PLoS One 7:e37282, 2012. Pubmed reference: 22615965. DOI: 10.1371/journal.pone.0037282.


Further information is available at Online Mendelian Inheritance in Animals.

« Back to the lexicon overview