Genetics of Curly Horses - Curly Mutations Identified!
A curly coat is a very characteristic feature of the American Bashkir Curly Horse breed, but can occasionally be observed in various other horse breeds such as Quarter Horses, Percherons, Arabians, Appaloosas, Missouri Fox Trotters, Tennessee Walking Horses, Paints, Morgans and Paso Finos.
The genetic background of this special coat has now been elucidated (nature.com/article). In the course of a DFG project, samples of Curly horses from all over Germany were examined at the Institute of Animal Breeding and Inheritance Research.
A total of two mutations were identified that are dominantly inherited and independently inherit a curly coat:
These mutations are located in the KRT25 and SP6 genes. A single mutated allele of the KRT25 variant or the SP6 variant is sufficient for the horse to develop the "curly" trait.
The dominant inheritance results in the following phenotypes with regard to curl expression:
AA- curly : Homozygote for KRT25- Many mustang horses show this mutation.
AG-curly : Heterozygous for KRT25- Many mustang horses show this mutation.
GG-smooth : wild type, no KRT25 mutation present
TT-curly : Homozygous for SP6- Many descendants of Curly Jim have this mutation; therefore occurs more often in Curly Foxtrotters
CT-curly : Heterozygous for SP6-Many descendants of Curly Jim have this mutation; thus occurs more often in Curly Foxtrotters
CC-smooth : wild type, no SP6 mutation present
Even though both mutations lead to a curly coat, there is an important difference between the two mutations. Horses with the KRT25 mutation also exhibit mild to severe hypotrichosis - a reduced number of hairs due to hair loss - whether or not they have the SP6 mutation. This explains the sparse hair coat in some horses from "curly" lines. In contrast, horses that only have the SP6 mutation do not show hypotrichosis.
The gene test offered can identify the KRT25 and SP6 mutations, which allow breeding selection for curly and full coat.