Inheritance of size

Horse and ponies come in all shapes and sizes. Domestication and intense selection has resulted in wide variation between breeds.

Work in humans has shown that height is controlled by a vast number of genes, each with only modest effect. What about horses?

Researchers at at Cornell University, New York, have been investigating the genetic control of equine size.

Shokouh Makvandi-Nejad and colleagues in the Department of Clinical Sciences, found that in horses, like other domestic mammals, a small number of genes was responsible for controlling size.
They conducted genome-wide association scans (GWAS) on DNA from 48 individuals from 16 breeds of both extremes of size, ranging from the American Miniature and Falabella to Shire, Percheron and Suffolk Punch, as well as 48 Thoroughbreds.

They found that genetic variation at just four points (“loci”) on the chromosomes could explain most of the variation in size between breeds.

The loci, on chromosomes 3,6,9,and 11, together accounted for 83% of the variation in size differences of the breeds in the study.

“Unlike humans, which are naturally reproducing and possess many genetic variants with weak effects on size,” the researchers comment “we show that horses, like other domestic mammals carry just a small number of size loci with alleles of large effect.“

“Furthermore, three of our horse size loci contain the LCORL, HMGA2 and ZFAT genes that have previously been found to control human height.”

They add that “the simplicity of the genetic control of horse size contrasts greatly with the complexity of human size genetics but is similar to results for the domestic dog.”
See: www.equinescienceupdate.com/articles/ioh.html