The A locus can be thought of as the gene that determines
if a horse is bay or black, although other genes come
into play. A horse that has at least one dominant "A" allele
will be bay if it also possesses at least one "E" allele.
A horse that is homozygous recessive for "a",
that is "aa", will be black if it also possesses
a "E" allele. All black horses are "EE
or Ee and aa". WHY TEST- If a horse is homozygous
for "e", it will have a sorrel or chestnut
base coat regardless of what genes it carries at the
A locus. Thus a chestnut horse may be able to produce
blacks if it carries an "a" allele and is bred
to another horse carrying the "a" allele and
a "E". If a person has a black horse and wants
to know if a breeding to a chestnut horse will produce
a black, the black horse needs to tested for the E locus
and the chestnut horse needs to be tested for the A locus.
A black horse that tests homozygous for "a" must
also be homozygous for "E" to produce 100%
We now offer the test for the mutation responsible for the Champagne factor in horses. The mutation was discovered here at the University of Kentucky. The Champagne gene is a dilution gene often confused with the Cream dilution gene. Unlike horses carrying a single Cream gene, Champagne horses have pink skin which becomes mottled in exposed areas such as the muzzle. Also Champagne foals are born with blue eyes that later darken to hazel or brown. A true black horse can mask the presence of the Cream gene, but a black horse carrying the Champagne gene is generally a chocolate color. There is no added effect if a horse carries two copies of the Champagne gene, whereas the homozygotes for the Cream gene create a more dilute horse with pink skin (cremellos and perlinos). Therefore the ability to test for the Champagne gene can distinguish homozygotes from heterozygotes, as well as more clearly determine the genotype of dilute pigmented horses.
The cream gene, designated Cr, is a dominant dilution
gene that causes a reduction in red pigment in the body
hair and mane and tail hair. It acts on any base color-
therefore a sorrel horse that inherits one copy of the
Cr allele is palomino (ee, Cr/cr), a sorrel that inherits
a Cr from each parent is Cr/Cr and is a cremello (ee,
Cr/Cr). A bay horse that inherits a Cr allele from one
parent is a buckskin (E/-, Cr/cr), while one that is
homozygous for Cr is a perlino (ee, Cr/Cr). True black
horses can mask the presence of the Cr gene, so it is
possible for a black horse to produce palominos or buckskins.
Cream is a different gene than Dun, which is also a dilution
gene. In general, dun horses have a dorsal stripe. WHY
TEST- Owners of a black horse with a palomino or buckskin
parent may want to determine if the horse carries an
unexpressed Cr allele. Horses carrying the champagne
gene may be confused with horses carrying the Cr gene-this
test will verify if the horses indeed possess the Cr
allele. It will also determine if a dun or gray horse
may also possess a Cr allele.
E locus (red gene)
The Extension locus is another gene related to color,
and determines whether a horse has black “points” as
in the bay coat color pattern (the mane, tail, legs
and tips of the ears are black). The allele responsible
for this pattern is designated as E, the capital letter
indicating it is dominant. The alternative
allele, e, is recessive, and when a horse has two copies
of this allele, as in ee, the horse lacks black pigment
in the extremities, as in chestnut horses. For
owners of a bay or black horse that want to know if
that horse is homozygous for the Extension locus, and
thus will always have offspring with black points,
a DNA-based test is available.
We now offer the test for the mutation causing the gray phenotype. Gray is caused by a dominant mutation, therefore a gray horse has at least one copy of the gray gene. Gray causes a horse to progressively lighten as it ages, regardless of other color genes the horse possesses. The ultimate effect is that the horse will become totally white or flea-bitten gray. The skin remains black unless the horse has other genes that result in pink skin. The test is useful to determine if a horse with two gray parents is homozygous for the mutation, or if a horse has such a dilute phenotype that it is difficult to determine if it also has the gray mutation.
Sabino is a Paint color pattern that is variably expressed
and can range from white stockings and a blaze to white
leg and face markings and extensive white spreading
up from the belly into the body area. The mutation
we detect is indicative of the Sabino1 gene. Homozygous
sabinos may have more extensive white than heterozygous
horses. There is more than one sabino gene so that
a horse that appears to have the sabino pattern may
test negative for the Sabino1 gene. So far all horses
that test positive for Sabino1 have the sabino pattern.
Silver Dapple (Z)
The Silver Dapple mutation results in a chocolate colored horse that has a lighter mane and tail. It is most commonly found in pony breeds and gaited horse breeds such as the Rocky Mountain Horse. The mutation requires the presence of at least one E allele to be expressed. Therefore genetically black or bay horses alone express it if they carry one or two Z alleles. A chestnut horse (ee) may carry a Z allele, but there is no effect on color. It is thought that horses homozygous for the Z allele have a whiter mane and tail than the heterozygotes.
The lab offers testing to determine homozygosity for
the Tobiano (spotted) gene. Since the tobiano color
pattern is valued and is dominant, horses that possess
two copies of the gene (homozygous) are of special
value to breeders, as ALL their offspring will inherit
the tobiano color pattern. We no longer perform the
serum protein test based on blood types due to its low
reliability. Instead, the University of Kentucky Animal Genetic Testing Lab is proud to offer the most reliable test for the Tobiano spotting pattern yet developed. Dr. Samantha Brooks of the University of Kentucky discovered an inversion on chromosome 3 that appears to be 100% concordant with the presence of the tobiano pattern. This test replaces the former double marker test previously offered. Please be advised that Tobiano testing reports will reflect this change.