Red Factor (Extension)

Quick Summary

The mutation causing red body and red trim (called sorrel, chestnut, or red) in donkeys has been identified in the melanocortin 1 receptor gene and is inherited as an autosomal recessive trait. 

Pair of sorrel Mammoth Jack donkeys
Pair of sorrel Mammoth donkeys. Image credit: courtesy of Mary Ellen Nicholas, from Equine Color Genetics, 4th Edition. Used with permission.

Phenotype: Donkeys described as sorrel, chestnut, or red have a red body and red trim.

Mode of Inheritance: Autosomal recessive

Alleles: Ed = Wild type, ed = Red

Breeds appropriate for testing: American Mammoth Jack, American Miniature, Normand; also appropriate to test when breeding mules

Explanation of Results:

  • Donkeys with Ed/Ed genotype will be wild type colored and cannot transmit this red variant to their offspring.
  • Donkeys with Ed/ed genotype will be wild type colored with black in the coat or trim, but are carriers of this red variant. They will transmit this red variant to 50% of their offspring. Matings between two carriers result in a 25% chance of producing a red foal.
  • Donkeys with ed/ed genotype will be red. They will transmit this red variant to all of their offspring.
Price

$25 one test per animal
$40 two tests per animal
$60 three tests per animal

Panels Available
Additional Details

Donkeys with red body and red trim are typically described as sorrel, chestnut, or simply as red. The locus governing this color is commonly called Red Factor or Extension. The mutation causing red in donkeys has been identified in the melanocortin 1 receptor (MC1R) gene and is inherited as an autosomal recessive trait. MC1R is also the gene that causes red factor (chestnut) in horses, but the mutations are different. Although both cause red/chestnut color, the donkey red factor is not the same allele as the horse red factor. Therefore, the horse test is not informative for donkeys and vice versa.

Red donkeys have two copies of the donkey ed allele. Donkeys with only one copy of ed, also called carriers, have black in the coat or trim. Breeding two carriers (Ed/ed x Ed/ed) has a 25% chance of producing a sorrel foal and a 50% chance of producing a carrier.

Genetic testing for donkey red factor is recommended for Normand, American Mammoth Jack, and American Miniature donkey breeds as well as for those breeding mules. If testing for red in mules, it is advisable to test for both the donkey and the horse red factors.

Turnaround Time
5-10 business days
Type of Sample

Species

Type of Test

Results Reported As
Test Result Red Factor
Ed/Ed No copies of donkey red factor. Animal is wild type color.
Ed/ed Carrier. One copy of donkey red factor. Animal is wild type color.
ed/ed Two copies of donkey red factor. Animal is red.
References

Abitbol, M., Legrand, R., & Tiret, L. (2014). A missense mutation in melanocortin 1 receptor (MC1R) is associated with the red coat colour in donkeys. Animal Genetics, 45(6), 878-880. doi: 10.1111/age.12207