HoistTheColors2.pdf

Hoist the Colors!

color genetics with lesli kathman

Pattern Interaction

Recent studies in the area of appaloosa patterning

have expanded researchers’ understanding of how

color genes can interact. In the next few articles, I

will discuss the many ways these patterns interact

with different base colors and modifiers. Looking at

these interactions is a great way to move past the

idea that colors and patterns simply overlay one

another.

within breeding groups, the Appaloosa Project was

able to use modern gene mapping to better analyze

information.

The missing piece - so often overlooked in early

studies - was the varnish roan pattern. Far from

being a separate, unrelated pattern, the Project

researchers found that varnish was the key to all the

other patterns.

But to understand those ideas, we’ll need to look first

at the basic mechanism behind appaloosa patterns.

Although the information is rather new, and the

studies are still ongoing, what has been learned to

date has a great deal of relevance to artists wanting

to paint realistic appaloosa patterns.

Prior Research and Assumptions

Earlier studies of the appaloosa patterns gave rise to

a number of theories. One of the earliest was that

blanket appaloosas were heterozygous, while

leopard patterned appaloosas were homozygous. A

later study by Dr. Sponenberg, done using Norikers,

indicated that leopards were heterozygous while few-

spots were homozygous. Varnish roan, which was

not thought to exist in the Noriker, was not part of that

study. It was assumed to be a separate pattern from

the one responsible for leopard. Yet another study

suggested it was possible to get almost any

appaloosa pattern from any other appaloosa pattern.

Needless to say, the information that was available

made for a confusing mess. For those that attended

my color seminars and wondered why the appaloosa

patterns were glossed over, this was why! None of

the theories seemed to fit the actual situation, at least

not well enough to inspire real confidence. How

could a blanket horse produce a leopard, or a varnish

horse produce a blanket? It seemed to me that

researchers were missing something - something

that could reconcile some (seemingly) contradictory

theories.

This Appaloosa mare shows the typical “varnish

roan” pattern - roaning that concentrates on the

rump, but leaves the legs dark. The high points of

the body usually remain darker as well, as can be

seen when the horse is turned at an angle from the

viewer (bottom). Small dark spots on the hips are

also common.

The Missing Piece of the Puzzle

Our understanding of appaloosa patterns took a huge

leap forward with the work of Sheila Archer and the

Appaloosa Project. Where older research on horse

color (my own included) centered around studying

the appearance of individual horses and trends

These include striped hooves, mottled skin and

visible sclera. It has often been stated that

appaloosas will always have these three things, and

that is true, though they are not always obvious. And

it is true because all appaloosa-patterned horses are

(genetically at least) varnish roans.

What leopard complex does not do, at least not on its

own, is add dense white patterning to the horse, nor

does it add dramatic spotting. The louder, highly

contrasting patterns so sought after by breeders are

the result of other genes that work with the leopard

complex gene.

Modifying the Modifier

The “Master Switch”

This is what has made the current theories about

appaloosa patterning so different from those in the

past. What has been proposed is that if leopard

complex (varnish roan) modifies the base color, then

there are yet another set of genes that then modify

the leopard complex gene. These modifiers are

collectively called pattern genes, and are given the

abbreviation “PATN” followed by a number.

Color genes are often likened to on/off switches.

What was discovered with the appaloosa patterns

was that there was a “master switch”. This switch,

when in the “on” position, made the whole range of

patterns possible. If that switch was off (i.e., if that

gene was not present), then none of the patterns

were possible.

The first of these has been labeled PATN1. This is

the gene responsible for the actual leopard pattern.

This is the pattern most past studies have focused

on, and it has been central in the work done by the

Appaloosa Project. It is believed, however, to be

just one of many patterns that interact with the

leopard complex gene.

The gene itself did not create the patterns. Or rather,

it created one of them; the one that had been ignored

for so many years. The “master switch” for all the

appaloosa patterns is the gene responsible for

varnish roan. Underneath whatever other patterns

are present, all appaloosas are varnish roans.

In fact, what has been most interesting about the

current research is just how many genes do interact

with leopard complex. Researchers expected to find

genes for the leopard and blanket patterns. What

many did not expect was that many more genes are

involved. The picture is actually much more complex

- as we will see in future issues of the Boat!

This gene has been named “leopard complex”, which

is usually abbreviated Lp. The name has lead to

some confusion, since the gene is not directly

reponsible for the leopard pattern. Instead, it is

responsible for the grouping (the “complex”) of

patterns that includes - and is best known for -

leopard.

Why the Varnish Base Pattern Matters

The important thing to remember, though, is that

appaloosas are all varnishes. Without a pattern,

leopard complex is varnish roan. If the horse also

inherits a pattern - say, Pattern 1 (PATN1) - he will

be a leopard. Genetically he’s still a varnish roan, but

the pattern gene he inherited transformed the varnish

pattern into a leopard.

So What Does the Leopard Complex Gene Do?

Leopard complex, or varnish roan, causes the coat to

progressively lighten in a distinctive pattern.

Typically a varnish roan will be lightest on the

hindquarters, excepting some small spots on the

hips, which are usually more densely pigmented than

the body. The darkest areas (aside from the spots)

appear along the high points of the body - the points

of the hip and elbow, the outer edge of the barrel, the

nasal bones, the ears - and the legs.

And because he is really a varnish, he’ll have the

traits that go with that. Just as a bay horse that has

begun to turn grey can still show signs of his base

coloring, so patterned appaloosas still show signs of

their base pattern. They have the striped hooves,

visible sclera and the mottled skin. The degree might

vary, but it will be there. In fact, if he inherits a

The leopard complex gene also creates what

horsemen refer to as “appaloosa characteristics”.

There is another factor besides the pattern genes

that can change the appearance of a leopard

complex horse. That’s because the leopard complex

gene is incompletely dominant.

Most horsemen are familiar with incomplete

dominance because of the cream gene. A chestnut

horse that inherits one cream gene will be a

palomino, while if that same horse inherited two he

would be a cremello. Leopard complex works much

the same way; horses that inherit two copies of the

gene will look different from horses with one.

The most basic difference is seen in the spotting.

Horses with one copy of leopard complex are

spotted. Horses with spotted blankets and leopards

are all carrying one copy of the leopard complex

gene. Horses with two copies of the gene are

(mostly) unspotted. These are the snowcap and

fewspot horses.

So a single varnish roan gene (Lp), when paired with

the leopard pattern (PATN1) might look something

like this:

Because varnish is progressive, many blanketed

horses roan out as they age. This horse, with his

clear white (not roaned) blanket, probably spent

some of his young adult life as a chestnut with a

blanket. Notice that his spots and the flash marks on

his legs are unroaned. Progressive roaning does not

effect the spots - which tend to be more deeply

colored than the body. That is why the original

varnish pattern is invisible on a “nose-to-toes”

leopard. All that is there is clear white and densely

pigmented spots - the two things unaffected by the

progressive roaning. (Photo graciously provided by

Lauren Olson and used with permission.)

pattern that leaves large areas of unpatterned body

color, those will eventually lighten just like the body of

a unpatterned varnish roan. This does vary, just as

the rate of roaning varies on regular varnish roans.

Nonetheless, high-contrast blankets with very clear

forehands - along the lines of the old Breyer Stud

Spider - can be accurately thought of as a temporary

phase in the pattern. Most will fade with age, leaving

the horse looking like a varnish roan with a blanket.

While that same pattern gene (PATN1) with two

copies of varnish roan might look like this:

Another Layer of Complexity

So appaloosa patterns depend on a “master switch”,

which, by itself, produces a pattern most equine

artists would know as varnish roan. It is also

responsible hoof striping, white sclera and mottled

skin. When that master switch is paired with

additional patterning genes, varnish roan is changed

to the louder blanket and leopard patterns.

And horse with the blanket pattern (PATN2) and one

copy of the varnish gene (Lp) might look like this:

Boosting and Suppressing

Varnish is modified by patterning genes like leopard

and blanket, and it changes based on whether or not

the horse has one varnish gene or two. There are

other factors which we’ll discuss a little more in future

issues, some of which boost the amount of white or

the number of spots. Others suppress the

expression of the patterns that are there. (My mare,

pictured in the previous article, has both. She has

sabino that can boost the white patterning, and a

suppressor that has reduced her leopard pattern

down to a large blanket.)

But beyond boosting and suppressing the amount of

white contrast, the appaloosa complex gene is

interesting because it alters almost every color or

pattern paired with it. This is what we will explore in

future issues.

And with that same gene (PATN2) and two copies of

the varnish gene, she might look like this:

Implications of the Research

For me, one of the most exciting things about the

Appaloosa Project research has been my belief that

the “master switch” concept is probably applicable to

the sabino pattern as well. In fact, we might just as

easily speak of that pattern as the “sabino complex”,

because we already know that it is not a single gene

but rather a group of related (and perhaps some

unrelated) genes.

There are other differences, too. Probably the most

important of these to a painter is that while the

hooves on dark legs of a heterozygous appaloosa

are striped, the hooves on the unmarked legs of a

homozygous appaloosa will be predominantly shell

colored. (Appaloosa legs with regular white markings

like socks and stockings will have ordinary shell

hooves no matter whether the horse has one copy or

two.)

It may be that with sabino, the “master switch” is the

gene for white markings, or more particularly, white

markings on the legs. We already know that in

breeds were sabino is not thought to be present

(British Shetlands, Gotlands), we don’t see

individuals with any leg white unless there is a pinto

pattern (tobiano in Shetlands, splash in Gotlands). It

may be that those breeds are missing that initial

gene, without which there can be no sabino pattern.

It is known that some sabino genes work as pattern

genes for leopard complex, so perhaps there are

pattern genes that can interact with a number of

different “master switches”.

The other interesting implication is that it is believed

that without leopard complex, the major appaloosa

pattern genes (PATN1 leopard and PATN2 blanket)

are invisible. Without leopard complex to “set the

stage” for them, they have no visible effect. If that is

the case, then we could have solid breeds carrying

around one of the ingredients for loud appaloosa

patterning. In fact, it would not be particularly

surprising to find these genes in breeds that have

had appaloosas in the past (Andalusians, Welshes,

Lipizzans) or who come from stock with close genetic

ties to patterned horses (Quarter Horses and Paints).

When horses have one of the major patterns like

leopard or blanket, then the presence or absence of

spots makes it pretty easy to tell whether the horse

has one or two copies of leopard complex. It’s a bit

harder with horses that don’t have an obvious pattern

gene. Many varnish roans do not have spots,

especially if the varnish pattern is very subdued. The

hooves are often the best clue, though those are

often hidden in pictures. (Hoof coloring is also hard

to determine in pasture-kept horses.)

This is of particular interest in those breeds where

varnish roan individuals have been found in recent

years - Walking Horses, Paso Finos, Welsh Mountain

Ponies and Andalusians. The varnish gene has, in

most of these cases, been obscured for generations

because it was paired with grey. It was also rare and

not especially sought-after. If these animals are used

in larger breeding programs, then their descendants

may one day get paired with a purebred carrying one

of those lost pattern genes. At that point, we could

see purebred leopard Welshes or Paso Finos.

So What Does This Mean for Artists?

In light of the new research, there are a few things

that artists need to keep in mind when painting

appaloosas.

1) The varnish roan pattern is fundamentally a

progressive pattern. Like grey, it lightens with age.

And like grey, care has to be taken that the stage of

the pattern fits to age of the model being painted.

Varnish is a lot more variable, and often progresses

much more rapidly than the typical grey horse, but it

is not a pattern seen on very young foals. Likewise,

it would be unusual to see a very old appaloosa with

no signs of roaning.

2) Spots are unaffected by the roaning. Regardless

of how much body color the horse loses as the

varnish roan progresses, the spots remain fully

pigmented. In fact, additional spots are sometimes

revealed (or develop) during the roaning process.

3) Spots are often more deeply pigmented than the

rest of the coat, even areas that are not yet roaned.

The spots are not, however, a different color from the

basic body color. (Painting black spots on the

blanket of a clear red bay is not accurate.)

Thumper, a miniature horse that lives at the barn with

my mare, is a good example of how varnish roan can

remain hidden in breeds not thought to have

appaloosa-patterned individuals. Last year, when

Thumper was five, his only pronounced roaning was

along his topline and rump. Everyone considered

him a bay roan. I thought he was a frosty roan,

which is a type of (true) roan that tends to

concentrate more heavily on the topline.

4) All horses with appaloosa patterns will have

appaloosa characteristics; mottled skin, sclera and

striped hooves. Like the roaning, though, these traits

develop with age. Few young foals show any signs

of mottling on the face, for instance. The traits can

also vary among individuals. The white sclera on

some appaloosas is ever-present, giving the eye a

human appearance even when the horse is

completely at rest, while others have eye whites that

are only slightly more pronounced than those of a

solid horse. Most people find extreme facial mottling

unappealing, so many breeders select for less visible

mottling. As a result, it is possible to find appaloosas

that do not look to have mottled muzzles, though like

the miniature horse pictured earlier, it can be seen if

the horse is examined closely.

At least, that was what I thought until - spoiled pony

that he is - he tried to give me a little nibble. That’s

when I saw his lips (left) and knew what he was.

After cleaning off his hooves (right), there wasn’t any

question. I would point out, though, that his hooves

were trimmed the day before this photo was taken,

making his stripes more visible. Prior to that it would

have been a lot harder to see. He is roaning out on

his face now, as his picture (top) shows.

5) Care should be taken that the hooves match the

pattern. Horses with homozygous patterns like few

spots and snowcaps should have predominantly

shell-colored feet. The more pronounced striped feet

are found on heterozygous horses with dark legs.

Appaloosa legs with ordinary white markings (socks,

stockings) will have shell-colored hooves just as any

other horse with such a marking would have.

Zygosity can be a difficult thing to assess, because

other factors can make a heterozygous horse look a

bit like a homozygous horse. But generally speaking,

it is better to paint the hooves shell if a horse is

predominantly white and mostly spotless.

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