BLOCKS TO COLOR!!
Here is a simplification
of equine color genetics that will help the beginner better understand how color
works in horses and also how better to identify colors and patterns in horses.
Not all the modifiers or dilutions will be covered here, but the basics that are
most commonly seen are.
When foals are born they have a baby coat that
is a different color or shade from what it will be as an adult. Sorrel and Chestnut
foals are usually born lighter than they will be as adults and their legs and
belly's are usually very blond in appearance. Quite frequently this light hair
is mistaken for stockings but true stockings will show a distinct line quite early
on in most cases. An easy way to be sure if a white marking is present is to wet
the leg and see if the skin under the light hair is pink or black. White markings
will always have pink skin beneath the hair. Foals have pink skin at birth so
you need to wait a week or so before trying to determine for certain.
foals are often born showing very little of the black that will signify it's points
later on in life. The best way to tell if a foal is going to be bay is to look
at the fetlock to see if there is black on it. Also the knees and hocks will generally
show some black hairs even though the legs will often times be very light in appearance
to begin with.
Black foals are often born looking gray, brownish
black, or black with silver or white guard hairs. Not many foals are born real
black looking all over. There are two types of black and both mature differently
but will look black at maturity.
It takes three to five years for
most coat colors and patterns to fully mature and in the case of gray and the
Appaloosa patterns the coat color and pattern change for the entire length of
the horse's life.
Champagne foals are usually born DARKER than they
will eventually be. They shed lighter and retain a dilute skin color. The skin
may be pink, tan, or light gray. Some are mottled or freckled in the skin. Champagne
horses also have diluted eye color which is most commonly amber but may be green
or gray. Champagne horses have reversed dappling with the dapples being lighter
than the coat color.
When horses are mated each parent contributes
ONE full set of genes to the offspring. The offspring then receives two copies
of every gene. In color, when both parents contribute the same gene such as red,
then that horse is termed HOMOZYGOUS for that color. That horse can then only
reproduce that color because it has no other choice available. When each parent
contributes a different gene then that horse is termed HETEROZYGOUS for that color.
That horse can then contribute EITHER color gene to it's offspring.
horses have to either be heterozygous for a color, or they have to be homozygous
for the color. To determine which they are there is a test available. The test
will tell whether the horse carries one or two copies of red or black.
does NOT matter what color the grandparents were because the colors do not skip
generations. They do appear to skip generations however. The color of grandparents
may be helpful when trying to determine base colors of horses that are dilute
or modified such as gray, champagne, or in some compounded colors where more than
one dilution is present.
To determine horse color one must FIRST
determine the base color of that horse. It will be either red or black. From that
base you can then determine what dilutions or modifications may be present by
it's own appearance, the parents, and in some cases the grandparents.
THREE BASIC TYPES
OF COLOR GENES
When a dominant gene is present
the horse will always be the color of that gene. The color "BLACK" in
horses is a dominant gene. A horse carrying the black gene will always look black
whether it has one black gene (Heterozygous) or two black genes (homozygous).
Heterozygous black horses have one red gene and one black gene so they can produce
EITHER Color in their offspring. Homozygous black horses can only produce black
foals no matter what they are bred to.
Recessive genes ONLY express
(show) when in the homozygous state. Both parents must contribute a copy of the
same recessive gene for the foal to express that color. The color "RED"
is a recessive gene. If a horse is red then it is automatically a recessive homozygote
and therefore can ONLY contribute a red gene to the next generation. When only
one copy of the recessive gene is present (Heterozygous) the horse will always
look the color of the dominant gene. Therefore if a horse has a black gene (dominant)
and a red gene (recessive) that horse will always appear black.
Polygenes are genes that require the assistance of other genes in order to
fully express. The resulting appearance will vary depending upon which helping
genes are present. Sabino is thought to be a polygene therefore it can express
in many different ways to many different degrees depending upon how many helping
genes are present. Because there are distinct patterns that form routinely under
the Sabino Gene it forms a complex of patterns.
In minimally expressed
sabinos the lack of helping genes may restrict the horse from developing more
than just common markings. If neither parent contributes the needed helping genes
for fuller expression, then the next generation cannot develop fuller patterns
unless the mate brings the helping genes back into play.
gene that creates the various types of patterns commonly called Appaloosa, is
also thought to be a poly- gene and forms a complex. The type and number of helping
Genes present determine what pattern the resultant foal will have.
The helping genes for the polygenetic patterns are each transmitted independently
Therefore a foal may inherit a pattern different from either parent.
COLOR MODIFIERS AND DILUTIONS
There are only TWO basic colors in horses (true white excluded).
The two basic colors are RED (recessive) and BLACK (dominant). ALL OTHER "COLORS"
ARE EITHER DILUTIONS of or MODIFIED from those two basic colors.
of these two things like this. Dilute colors are like what occurs when you pour
cream into coffee and stir it up. You cannot tell where the cream starts and the
coffee ends because it all becomes one. With dilute colors the hair itself is
lightened to a paler shade of the base color so you will not see the base color
Now think of the Modified colors as sprinkling sugar or salt
on a colored mat. You still see the colored mat but the salt or sugar coats it
in a way that makes the overall appearance lighter. Light modifiers such as roan
or sabino add white hairs to the coat. They mingle with the base colored hairs
to produce an overall lighter appearance to the coat.
work similar to the light. Think of sprinkling pepper on a mat. The color of the
mat is still there but the pepper makes it appear darker. Sooty is a dark modifier
and can be found on any color horse with the possible exception of champagne,
maximum white sabino, or dominant white. It can be seen minimally in perlinos,
cremellos and though muted may deepen the tone of the body hair or form dapples.
color is a color that has been altered itself. The pigment within the hair shaft
has been altered so that it no longer is as strong or deep in hue as the basic
hair color. Some color dilutions can work to dilute all colors while others only
work on one specific color or area of the body. Some examples of dilute colors
are palomino, smoky black, buckskin (from one copy of the cream gene) cremello,
smoky cream, perlino( from two copies of the cream gene); amber champagne, golden
champagne, classic champagne ( from one copy of the champagne gene) Ivory champagne
( from either two copies of the champagne gene or one copy of champagne AND one
copy of cream); Red, yellow, silver, coyote Dun, grulla, (caused by one or more
copies of the Dun gene) Agouti which dilutes only the black on a black horses
body to make that horse a bay. And finally Silver dapple which also only expresses
on black but can be carried in red horses.
MODIFIED color are colors
that appear different due to the mixing of white, light, or darker hair with the
basic hair color. Some modifiers only act on mane, tail and point colors while
others work on the entire body color.
Examples of modified colors
are true roan where the body color of the horse mixes about 50/50 with white hairs,
Gray...although this is really a dilution of hair color it falls under the Modified
rule because eventually the hair of the horse will all turn white.; Sabino, white
hairs will mix with base color to varying degrees which can cause only a light
ticking or full blown roaning but in sabino roans the face and lower legs will
also be roaned.
Some examples of Modifying genes are:
GRAY, AGOUTI, SOOTY which adds dapples, darker hair on knees, hocks, bony prominence
of the face, and can make entire body coat darker including manes and tails;
of dark modification are Black Bay, Sooty palomino, sooty buckskin, or any other
color that is dark due to the mixing of dark hairs along with the basic hair color.
Often this modifier will cause dark dapples to appear, barring on the legs, shoulder
and counter shading on the back. Dark modifiers are usually called SOOTY, or SMUTTY.
They can also cause such things dark smudges on the boney areas of the face.
There are four basic spotting pattern genes:
Tobiano, Frame, Splashed White, Sabino.
Early in embryonic life all
foals are white. Pigmentation begins at the stem cell and works along the spine
then down the trunk of the animal until it is all colored. When this process is
interrupted the result is that area where the pigmentation did not occur will
There are four specific genes that cause these interruptions
to occur and each one acts in a way specific to itself.
when they are pure of other spotting genes, tend to have little white on the face
and legs. They will have crisp edges to the patches of color and the body will
generally be 50% or more colored. Today in the Paint horses and other breeds many
of the horses called Tobiano actually have more than one spotting gene present
but because the registry will only recognize one pattern on the papers, Tobiano
is used exclusively unless that horse looks more like one of the other patterns.
Tobiano's will always or almost always, have some white cross over the spine.
Tobiano is a DOMINANT gene. If it is present it must express itself, but it can
express so minimally that it goes undetected. Some minimal Tobianos will only
have perhaps a small sock with ermine spots in it as an indication of the gene's
True Tobianos usually have solid faces or at best minimal
face markings. Tobianos also tend to have solid colored legs or minimal white
on the legs. In the Paint breed, as well as in the Fox Trotter and Tennessee Walking
horse the addition of Sabino and other spotting patterns have melded to make Tobianos
appear to have louder markings. Once the two genes merge they generally reproduce
together as well. Whether this is a partial mutation is unclear at this time.
OVERO IS NOT A COLOR
Tobiano are a group of patterns commonly and very MISTAKENLY termed "OVERO".
There is no Overo gene and therefore the term is very antiquated and should be
abolished because it causes a good deal of confusion when it comes to identifying
spotting patterns. Because of this antiquated term most people do not understand
that what is termed "overo" incorporates three totally unrelated genes
representing distinctly individual patterns which have their own set of "rules"
and in some cases problems.
The three patterns which are mistakenly
termed "overo" are Frame, Sabino, and Splashed White.
horses tend to have a lot of facial white but their spots are generally limited
to the sides of their body leaving their back and belly colored. Therefore the
color forms a "frame" around the white. Smaller spots on the neck will
be surrounded by pigmented skin. Frame horses often have blue eyes. Frame pattern
is the ONLY PATTERN to cause Lethal White foals and then only in the homozygous
state. A foal MUST receive the OLW gene from BOTH parents in order to be a Lethal
White. A simple test can be made to see if a horse carries the OLW gene. IF it
does, then by simply breeding it to a OLW negative horse you eliminate the possibility
of producing a Lethal Foal.
Frame is a DOMINANT gene but it can express
so minimally as to go undetected. It is unclear at this point what the most minimal
expression is for this gene because some solid appearing horses test positive
for OLW which means they carry the Frame gene.
SPLASHED WHITE horses
are horses who appear to have been dipped in white paint. Their markings are very
clean cut and usually quite level looking rather than sharply pointed or lacy
at the edges. Splashed white horses are basically white on the bottom half and
colored on the top. Facial markings are usually bald or apron faces but the top
of the markings are usually clean cut horizontally often leaving the ears and
skull cap colored. Legs and belly markings are usually very even and lack irregular
edges. There is a connection between deafness and the Splashed White pattern and
of all the spotting patterns Splashed White is the most rare. It is unclear whether
Splashed White is a dominant or recessive gene or perhaps a poly-gene.
all horses with sharp lines or flat lines of color are splashed white! It takes
more than just a face or leg marking that is level to make a horse a splashed
SABINO is thought to be a poly-gene which can cause as many
as 19 or more specific patterns forming a complex. There are also many variations
or mutations of the Sabino gene that have been identified.
how many and which helping genes are present, Sabino can express any way from
just a solid horse with a few scattered white hairs all the way up to a solid
white (viable) horse with dark eyes. In between those two extremes are a host
of patterns such as common white markings, high white markings, belly spots, sabino
roan, loud sabino (spotted) and medicine hat.
Today, many Sabino
horses are mistaken for Frame, Splashed White and even Tobiano because Sabino
can mimic all of those patterns. Perhaps the most commonly recognized pattern
for sabino is the high white or loud patterns. The high white pattern is what
you see in the Clydesdale Budweiser team where the horse has long stockings over
the knees and loud facial white.
In most instances Sabino horses
have irregular edging to their spots and there will generally be some roaning
involved in the colored areas of the pattern. That roaning may range from just
a few scattered white hairs to fully roaned patterning and in some cases the roaning
can be so extensive as to make the horse nearly white in appearance.
mutation of Sabino, particularly found in Arabians, often produces sabino patterns
that are very crisp and lack roaning. The edges to the white markings are sharp
rather than irregular or feathered.
Sabino is the most prevalent
of all the spotting genes and yet the least recognized or understood. When Sabino
is present along with another spotting gene it will nearly always add white to
the pattern of the horse.
Typical pattern markers for sabino will
be long white stockings that sometimes run up over the knees or hocks and often
come to a point. Disconnected lightning strikes on the upper leg, leg spots, belly
spots and white on the head that runs down to the lower lip, chin or under jaw.
Roaning or ticking is nearly always present but may not show up until the horse
In less typical patterning, however, sabino can express
in quite a crisp fashion with sharper edges to the spots and more even leg markings.
Research conducted recently has identified at least one form of
sabino. There is a test for the SB 1 sabino pattern now available. The "high
white/roaning" genetic marker has been identified but so far only one mutation
of the sabino gene has been located. The research done on the SB1 gene has shown,
however that there are at least 5 variations or mutations of the sabino gene in
modern horse. The SB2 test should be available in a relatively short time. There
is a mutation called Draft, a specific mutation in Arabians, and one thought to
be in Thoroughbreds that differ from the SB1 type even tough they can produce
similar patterning. Homozygots for the Sabino gene have been identified.
in the gaited breeds, Paints, and some of the Spanish breeds, Sabino is mixed
with other patterns or mistaken entirely FOR those other patterns. In particular
Splashed White or Frame. In part this is the fault of breed registries that only
allow one pattern to be identified on the registration papers.
foals born from Sabino action are totally viable and healthy yet each year many
are destroyed from being mistaken as Lethal Whites Frame.
There is another spotting gene in horses
that is different from the "Pinto" or "Paint" patterns. This
gene is the LEOPARD gene. The patterns caused by the Leopard gene are typically
called the Appaloosa patterns. Similar to the Sabino gene, the Leopard gene is
thought to be a poly-gene and forms a complex of a variety of patterns. Snowflake,
Varnished roan, Blanket, and Leopard patterns are a few of the more common Appaloosa
patterns caused by the Leopard gene.
Horses with the Leopard
gene often display mottled skin, striped hooves, and sometimes a white sclarea
around the eyes and may be born solid color only to pattern out as they mature.