UC Davis School of Veterinary Medicine Veterinary Genetics Laboratory
Red Factor

Order this test on MyVGL

The Extension gene, also known as melanocortin 1 receptor (MC1R) or Red Factor, has three alternative states (alleles). The dominant allele E produces black pigment in the coat. The recessive alleles e and the rare ea produce red pigment (red factor). The rare ea allele is known to occur in Black Forest and Canadian horse breeds. Red horses (chestnuts, sorrels, palominos and red duns, to name a few) have two copies of a recessive red allele (e/e, e/ea or ea/ea). Horses capable of producing black pigment (black, bay, brown, buckskin and grullo, to name a few) have at least one copy of the E allele. They can be homozygous E/E or heterozygous E/e or E/ea. A horse that is homozygous E/E will not produce red offspring, regardless of the color of the mate.

The DNA diagnostic test for the Extension gene helps to determine the base color of horses and can be used to identify those black-pigmented horses for which neither pedigree nor breeding records is informative for identifying carriers of the recessive red factor. Since red is inherited as a recessive trait, it is relatively easy to start up a breeding program that will produce only red horses. Results from the DNA test help breeders to determine the genetic make-up of the Extension gene in breeding stock to choose appropriate mating pairs to establish a breeding program to produce only black-pigmented horses.

Results are reported as:

e/e

Only red factor detected. Basic color is red in the absence of modifying genes.

ea/ea

Only red factor detected. Basic color is red in the absence of modifying genes.

e/ea

Only red factor detected. Basic color is red in the absence of modifying genes.

E/e

Both black and red factors detected.

E/ea

Both black and red factors detected.

E/E

No red factor detected. Offspring cannot be chestnut/sorrel.

References

Marklund L, MJ Moller, K Sandberg and L Andersson. (1996). A missense mutation in the gene for melanocyte-stimulating hormone receptor (MC1R) is associated with the chestnut coat color in horses. Mamm Genome 7: 895–899.

Wagner H-J, M Reissmann. (2000). New polymorphism detected in the horse MC1R gene. Animal Genetics 31:280-291.

 
Veterinary Genetics Laboratory, Tel 530-752-2211, Email VGL