Coat colour E locus / chestnut / red factor (MC1R-related) - Horse

What does this test analyse?

This genetic test detects the MC1Re allele with variant c.248C>T. This trait is known as E locus, extension, red factor, chestnut, sorrel or red coat colour in horses.

The E locus determines whether a horse can produce black pigment in the coat and points. The dominant E allele allows black pigment. The recessive e allele restricts pigment production to red/yellow pigment. A horse with two e alleles is chestnut, even when other loci would otherwise be able to distribute black pigment.

Why is this important for colour planning?

A horse that is not chestnut can still carry an e allele. This means that two non-chestnut horses can produce a chestnut foal if both parents pass on e. Conversely, an e/e horse cannot show black pigment in the coat, which changes how other colour genes become visible compared with a horse that has at least one E allele.

This test is especially useful when coat-colour expectations matter for breeding goals, sale, registration, mare selection or stallion selection. The result also helps interpret other colour tests, such as A locus, Cream, Pearl, Champagne, Dun or Silver, more accurately.

Practical value of this test

• Breeders can better predict whether a mating can produce chestnut foals.
• Hidden carriers become visible, even in horses that are black, bay, brown, buckskin or another non-chestnut colour.
• The test helps explain why certain colours keep appearing in a line or appear unexpectedly.
• For colour planning, the E locus result can be combined with A locus and dilution genes to create more realistic foal-colour expectations.
• For sale and communication with owners, a DNA result gives more certainty than appearance or pedigree alone.

Inheritance and result

The e allele is autosomal recessive. A horse with E/E does not carry the tested e allele. A horse with E/e is a carrier and can pass on e without being chestnut. A horse with e/e has the genetic basis for chestnut/red coat colour. The final shade, intensity and possible dilution still depend on other coat-colour genes.