| Basic Building Blocks of Horse
There are 3 basic color
"building blocks" in horses that are controlled at 2 genetic locations.
The Extension locus determines whether or not black pigment is present.
Black is dominant at this locus and red (chestnut) is recessive. Horses
will either be
EE (homozygous black), Ee (heterozygous black) or ee (chestnut) at this
locus. The second locus is the Agouti locus which determines whether
pigment, if present, will be expressed throughout the coat or
to the points (bay). All dilutions (creme, champagne, silver dapple)
patterns of white (roan, gray, tobiano, sabino, frame, splashed white,
act on these basic color building blocks.
Then there are various shades
that come from the action of sooty or pangare (mealy) modifications.
geneticists believe that seal brown is probably the action of sooty on
chestnut or pangere on black, though there is still some possibility
there is a separate gene for it. There is also some possibility that
may be a "jet black" in addition to a "fading black." There's still
to learn, and most of it is still theoretical, but they have developed
a DNA test to determine what the genetic make up of a particular horse
is at the Extension locus. That test determined that our stallion Color
Master is EE, or homozygous black, and our filly MeMe is Ee, or
sabino, or both?
Both roan and sabino are
patterns of white imposed on the horse's base color, but they are
caused by two different genes. The roan gene causes white hairs to be
mixed in with
the base coat color on the body and neck. The head and legs remain the
base color. Roans go through seasonal changes, with more white during
spring, somewhat less in the summer, even less in the fall, and less
in the winter.
Sabino is one of several
"spotting" genes. In the Paint breed, "spotted" horses are divided into
two types, tobiano and overo. In recent years, however, it has been
demonstrated that "overo" is actually made up of at least three
separate genes: frame, splashed white and sabino. The Missouri Fox
Trotting Horse Breed Association, like many breed registries, has
followed the Paint definitions for spotted horses and so only recently
recognized "sabino" as a pattern.
Sabino is characterised by a wide
blaze which may extend onto the lower lip, high white stockings which
often have extensions above the knee and hock, white splashes,
on the belly, and often by roaning of the coat. A lot of confusion has
come from the fact that the sabino pattern can be minimally expressed
our foal MeMe) with only a few white markings and some roaning, or
maximally expressed as a medicine hat or even all white horse (like
In 2004 we were asked to participate in a study at the University of Kentucky hoping to isolate a gene or genes responsible for causing the sabino pattern. It was thought that maximum sabinos and their offspring could be especially helpful in the study. We sent in DNA samples from Color Master, our sabino mare Travelin' Tootsie, and their son Rhythm Master. The study did identify a gene, Sb1, which causes a sabino pattern, but it is thought to be one of many sabino patterns. Color Master tested as homozygous for Sb1, so all of his offspring will have a copy of Sb1 and will be at least minimla sabinos. As expected, Travelin' Tootsie tested as heterozygous for Sb1, meaning that she is sabino but has only one copy of the gene, and Rhythm Master also tested heterozygous for Sb1. The study confirmed that horses that are homozygous for Sb1 will be white or nearly all white. Horses can have a copy of Sb1 and still be very minimal sabino. Since Color Master is homozygous for Sb1, that means that even his most minimally marked offspring are indeed genetically true sabinos.
Travelin Tootsie, is a "classic" sabino.
| Notice the speckling on her head, and how her blaze
extends down onto her lower lip. She also has a small spot on her
shoulder that is covered by her mane. The speckled, "lacy" appearance
of her leg markings is also quite typical of sabino, and so is the way
her stockings come to a point. Tootsie's registration papers identify
her as a red roan, but she is clearly a sabino.
| Our stallion, Color Master, appears at first
glance to be a white horse. However, his white color comes from the
of the sabino gene. His sire is a black sabino and his dam is a bay
you look closely at Color Master, you can see that he has black spots
his otherwise pink skin around his eyes, on his ears, on his chest and
flanks, under his tail, on the insides of his back legs, and on his
These spots have been getting darker and more numerous over the last
and he's also getting a few black hairs over some of those spots and in
his mane and tail.
Color Me Tootsie, our filly by Color Master out of Travelin' Tootsie, is a very minimal sabino. She has only an unusually
shaped star and snip, lots of roaning, and some small spots on her
lower legs and lower jaw. The
far right shows the roaning on her rump.
true roans have very minimal white markings other than the roaning.
heads are generally darker than their bodies, and their color exhibits
seasonal changes. Roans are generally lightest in the spring and
in the winter. Our mare Warrior's Yankee Lady is a bay roan. She also
the "frosty" roan pattern, which means that she has white hairs in her
and tail, and her roaning is somewhat uneven, with darker and lighter
patches. The pictures that follow show her seasonal color changes, from
almost white in spring, to a sleek silvery pink in summer, to a darker
silver in fall
and almost solid bay in winter:
Tate in spring
Tate in summer
Tate in fall
Tate in winter
Warrior's Yankee Lady had her first foal in 1999, we thought at first
filly was a bay sabino, since her sire carries the sabino gene.
within the first few weeks of her life, the filly began to exhibit the
seasonal color changes of a roan, and it became clear that she carries
Lady at birth
Lady as a yearling