Download Appaloosa Inheritance

SOME THOUGHTS ON THE INHERITANCE OF WHITE EXTENSION
IN THE APPALOOSA
Introduction
This is merely a theory on the Appaloosa horse coat marking inheritance, based on genetic information
gleaned from other animals over many years (in particular for the type of dog I have bred for nearly thirty
years in which any colour and marking goes), studying horse colour genetics in general, taking numerous
Appaloosa pedigrees back to ‘unknowns’, scrutinizing photos, and receiving comments from Ap breeders on
both sides of the Pond over two years or so.
Particular thanks to Mel Pritchard (UK) who graciously put up with my continual bombardment of
questions, and unstintingly gave me full details of her Ap stallion’s breedings for 2005 foals (18). My foal
predictions scored 61% for exact base colour and 56% for exact and ‘to one place’ markings. I was way out
on three markings that provoked more study and enabled me to tweak my ‘spotty’ theories further.
I realise that some of the following is controversial but until such time as other theories or genetic proof can
be read without somebody saying “I’ve experienced, or actually know, differently”, the more expressed
thoughts the better for the layman to consider and plot his breeding course in the interim I feel.
NB. Not finding much information on Appaloosas having dark spots without white backgrounds, this aspect
has not been included, which does not mean to say it has no significance.
Basis of Heredity
The horse, like all animals, is made up of innumerable minute cells. Each cell has a major area of cytoplasm
(largely proteins) with a centre area known as the nucleus. The nucleus contains the genetic rod-shaped
material called chromosomes. The horse has 32 pairs of chromosomes, those belonging to a pair are known
as ‘homologous.’ Paired genes are situated along the length of each chromosome and are the source of DNA
– which holds the myriad of complex genetic information and instructions that are the basis of heredity. One
member of the homologous chromosomes comes from the sire, one from the dam, so too each member of
the gene pairs. Genes in the same position (locus) in homologous chromosomes influence the same
character/s but can influence in different ways; these alternatives are known as alleles (‘ah-leels’) of a gene.
There can be many alleles of a gene but only two at any locus. If the two alleles at the locus are identical
(influence the character in the same way), an individual is called homozygous for that character. If the two
alleles are different, an individual is called heterozygous for that character.
Recognised Markings Found in the Appaloosa
Mottled:
Mottled skin pigment/white eye sclera/striped hooves. The minimum expressions
(characteristics) of appaloosa markings, which should accompany white coat markings.
Few Spot:
Born white with a very few small base colour spots over body, with or without minimal
shin markings. No other coat markings.
Snowcap:
Ranging from solid white splash on hip, through white blanket, to part extension leaving
head/neck/legs/’armpits’/mane/tail base colour with a very low percentage of base colour
spots. (Fully extended: born white with a very small amount of base colour).
Leopard:
Born white with numerous base colour spots over entire body, ranging from small spots
to very large (Loud Leopard). Base colour remaining on head/neck/legs/mane/tail
described as “Near Leopard.”
Spotted Blanket: Ranging from white over hips with numerous base colour spots within, large or small,
extending forward to withers.
Snowflake:
Small white spots on base colour, ranging from one area of the body to whole body,
sparsely sprinkled or intense.
-2-
Frost:
Ranging from a scattering of white hairs over hips, extending forward across the top half
of the body and downwards to midline.
Varnish/
‘Roan’/Marble:
NonCharacteristic:
Progressive ‘roaning’ often first apparent on the forehead of the foal, and covering small
areas or to full extension, leaving base colour marks over prominent bones but not
necessarily disguising any existing markings.
Solid base colour from Appaloosa breeding, with or without standard white face
markings/socks.
Solid:
Solid base colour of non-Appaloosa, with or without standard white face
markings/socks.
Sabino:
Ranging from a white chin spot and/or white foot/feet with diminishing spear edge, to
white patches which appear to run vertically up legs, under belly and neck, with large
ragged splashes, spots, bald face and coat ticking. Blue eye/s can occur if blaze runs
near or into eyes. (Fully extended: born white with a very small amount of base colour.)
Many Appaloosas display minimum and moderate sabino pattern.
Mottled Skin
Few Spot
Near Leopard
White Eye Sclera
Striped Hoof
Leopard
Spotted Blanket
-3-
Snowcap
Extended Snowcap with sparse spots
Moderate sabino white spotting pattern
Extended Snowcap
Varnish/’Roan’/Marble
Sabino ticking
Appaloosa Colour
The term ‘appaloosa’ is recognised globally as a coat pattern, and is now applied to breeds not associated
with that founded by the Nez Perce. Whilst the crossing of various types, colours and coat patterns is how
most animal breeds evolve, they then need to breed true to themselves to unify and purify that breed, and set
it apart from others. They will get to a genetic point where every offspring will inherit an own-breed gene
from each parent and therefore achieve true pure breed status, displaying exclusive characteristics. The Nez
Perce achieved this over the 170 years or so prior to the devastation, allowing the breed a genetic marker.
Speed combined with stamina would have been one of the characteristics, sureness of foot over varying
terrain, scanty mane and tail, Indian Shuffle gait, others.
Coat colours in the Nez Perce Horse were reported as ‘red’ or black with a smaller portion displaying white
spotting, commonly spotted blanket, often ‘roaned.’ There was, significantly, little other white markings or
any dilute base colours.
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Some consider all modern-day ‘Western’ Appaloosas to be a breed in their own right but, as registered
purebred Thoroughbreds, Quarter Horses and, more recently Arabians, are commonly accepted as
‘outcrosses’ by most Appaloosa registers, ‘purebred Appaloosa’ can only be applied to those individuals
who have inherited an appaloosa gene from each parent – that is, at least one grandparent on each side of
their pedigree will need to be an Appaloosa for the chance of this to occur. The Foundation Appaloosa
Horse Registry (FAHR) <www.foundationapp.org> recognised this fact in 1997 when Appaloosas of 5generation purity were almost extinct, and is moving towards this level of pureness once again, only
registering Western Appaloosas with no more than one great-grandparent a non-Appaloosa (one horse out of
fourteen immediate relatives) plus two other great-great-grandparents, allowing a minimum 75% purity – a
method already proven in other registered breeds. Additional white markings/blue eyes are restricted (e.g.
sabino). Another North American Appaloosa register has since allowed sub-registry to this end, but using
different criteria. Some countries have closed their books to future crossbreeding, but with spotted nonWestern derived horses contained within. However, unless linebreeding is practiced, or similarly
constructed individuals bred together, type will be greatly varied. Even so, the evolving North American
purebred Appaloosa will be a different type to those evolving in other countries.
The appaloosa marking is referred to as ‘colour’ by enthusiasts but is more correctly the extension of white
through colour. Most white spotting patterns in the horse are inherited in a dominant fashion and then
believed dependent on the inheritance of a certain threshold of associated favourable minor modifying genes
for the expansion of white; the inheritance of Plus and Minus modifying genes discouraging/enhancing the
production of white. The Appaloosa adds a twist as its spotting pattern is so varied which renders the
inheritance more complex, allowing colour to be easily lost, weakened, or ‘masked’ within a couple of
generations. No surprise as Nature frowns on unpigmented skin, which coat spotting encourages, and will
do its best to revert spotting back to an acceptable level to survive in the wild state – unpigmented skin
adversely reacting to parasites, insects, allergies, disease and extreme weather.
It is already known that, from the two pigment colours of the horse, the recessive red (chestnut and its
dilutes) allows spotting to be more readily expressed; likewise certain variations of the dominant black
pigment suppresses it.
A horse not of Appaloosa lineage but of other spotted lineage, not necessarily spotted itself, can encourage
expression of appaloosa markings from its Appaloosa mate - sometimes allowing both clearly defined
patterns as seen in the ‘Pintaloosa’ (Pinto and Appaloosa breeding).
The expression of white markings can also be influenced by non-genetic factors, with studies into white
facial markings in the Arabian showing the latter as much as 32% for example.
(Spotting patterns in the horse range from regular/irregular spots to regular/irregular patches of base
colour in various ratios to the white.)
Here, the Appaloosa Breed is represented genetically ‘Ap’, and Solid breeds represented ‘S’.
Lack of Colour
Whilst the Non-characteristic ApN is arguably no longer an Appaloosa as it has the same phenotype (what
you see before you) as true Solid, it can serve to carry the ability of contributing white markings to the next
generation from its genotype, i.e. it has the means to process appaloosa markings ‘hidden’ in its genes.
There is evidence to suggest that certain compilations of the A and E gene Series give rise to the Noncharacteristic. The purebred Non-characteristic may therefore play a more important role than realised
within the Breed, in passing on strong colour when its dominant compilation is ‘broken,’ releasing its
amassed store of favourable white modifiers to its offspring.
-5-
However, if a ‘Non-characteristic Appaloosa’ inherited Solid from both parents (e.g. they each having a true
Solid non-Appaloosa parent themselves), the ‘Non-characteristic’ would in fact be true Solid and unable to
contribute white to the next generation. In effect, it is this ‘Non-characteristic’ that is no longer an
Appaloosa; but it could parent a coloured foal in the same way as other Solids can, if mated to an Appaloosa
of suitable colour and sufficient favourable modifiers.
High Colour Producers
Claims for Appaloosa stallions throwing 100% colour are always subjective to the markings and breeds of
their mares and the number of progeny. Such claims for, say, ten progeny will not be as accurate as for 100,
the latter being the genetic benchmark. Even the pure Appaloosa, i.e. the horse that has inherited an ownbreed gene from each of its parents, cannot be guaranteed to produce colour on all mares.
The almost white Few Spot nearly always produces within the range of appaloosa markings, including to
solid, so is dominant to a high degree. In a very few cases, Non-characteristic/solid has dominated Few Spot
for expression.
The Snowcap is treated by enthusiasts in the same vein as the Few Spot, i.e. a very high colour producer of a
dominant nature. Its origin could be a mutation of sabino, a dominant spotting pattern found in an
influential smooth-gaited English breed of medieval times.
(Sabino of minimal and moderate expression is now in most breeds, with title believed to be Spanish or
Italian. Accompanying ticking is very common and can easily be confused with Appaloosa ‘roan.’)
Leopard may have its origin in Dominant White W (giving rise to mottling of skin and hoof), via the spotted
horses depicted in Persian art of the 6th century. Few Spot may well be a composite of Leopard + Snowcap
+ App roan + sabino and could be represented by ‘ApW’.
A Leopard, born white with distinct, small to medium-sized spots may be a higher colour producer than a
Near Leopard with large spots although it will be the latter who looks more the part because of its soughtafter ‘loudness.’ It’s interesting that colts via a Snowcap parent appear to colour better than fillies, but both
appear on a par from a Few Spot parent.
Whilst they are generally grouped as the Few Spot/Snowcap continuum, it would be wise to consider the
Few Spot and the Snowcap separately, even though they braid well and have similar high colour production
rates, in so much that Snowcap is a singular appaloosa coat marking whereas Few Spot could be a composite
which includes Snowcap.
If the Snowcap has its origins in the dominant sabino, it could also be ApW, differentiating ApWF (Few
Spot) and ApWSC (Snowcap).
Unfortunately extended Snowcaps are often described as “few spots” so it is very difficult to gather separate
factual information. Fact does show that Few Spots are not necessarily the produce of two Snowcaps, and
can be from non-Few Spot Appaloosa parents (but of Leopard and Snowcap lineage themselves).
The content of Leopard, Snowcap, App roan and sabino from both sides of a pedigree would be needed to
express the Few Spot pattern; Snowcap or Snowcap and Few Spot to express the extended Snowcap pattern.
This would ensure the inheritance of the minimum favourable white modifying genes required for the
expression of these two particular ApW patterns. It would be interesting to know if the Snowcap and Few
Spot appeared in the Nez Perce Horse, or whether they came later when it was crossbred after 1877.
Some homozygous extensive spotting in other horse breeds carries lethal and delayed lethal genes, and
various disabilities, so is avoided. In other animals, lethal genes and disabilities are known to be ‘held’ in
the white specimen if some base colour is evident at birth, if only to fade out later. Some breeders of white
-6-
Persian cats believe a birth spec of base colour between the ears indicates the avoidance of associated
deafness for example. The extended Snowcap could well avoid immediate lethal conditions as it is born
with base colour to its extremities.
Sabino-white very occasionally occurs in most horse breeds and varieties, including recognised solids such
as the Thoroughbred – born white, sometimes with a very small amount of base colour on poll/ears/mane/tail
that can fade, mostly dark-eyed – but can be purposely bred from selective sabino x solid and sabino x
sabino matings. It probably exists in the Appaloosa, and could mimic a fully-extended Snowcap. A sabinowhite Appaloosa would not allow any coat spots or stripy hooves to appear and skin pigment, if present,
would not be in typical fashion. Sabino-white is subject to sensitivities of skin and other organs, but not
believed to carry immediate lethal genes in homozygous form.
In effect, there would be three genetic types of dark-eyed ‘all-white’ purebred Appaloosa:



Sabino-white – Producing itself or any appaloosa marking, including Non-characteristic. Always
producing some degree of Sabino marking.
Fully-extended Snowcap – Producing itself or any other appaloosa marking, including Noncharacteristic. Predominantly producing Snowcap Sequence, i.e. Fully-extended Snowcap,
Extended Snowcap, Snowcap, Minimal Snowcap (e.g. small white hip mark).
Few Spot – Producing itself or any other appaloosa marking, including Non-characteristic.
Predominantly producing Leopard Sequence, i.e. Leopard, Nr Leopard, Extended Spotted Blanket,
Spotted Blanket.
Both the Few Spot and the fully-extended Snowcap can also have Sabino minimal or moderate
markings and/or Appaloosa ‘roaning.’
All Few Spots are believed to suffer from Congenital Stationary Night Blindness (CSNB) to some degree. It
is not known the depth of night blindness in the Snowcap but extended Snowcaps (at least) do readily appear
to suffer the condition too (in other horses it is expected that 1 in 16 will suffer night blindness). Lesser
white-marked Appaloosas may or may not suffer the condition.
My own vet, the respected eye specialist Ian Mason, suggests a good place to start a DNA search for this
defect in the Appaloosa is with another animal species – the Briard, a large, long-coated, dark eyed French
sheep herding/guard dog dating back to the 8th century who also suffers CSNB. The defect has already been
genetically marked and there is a DNA test available to this Breed, the mode of inheritance of a recessive
nature with advice not to breed from affecteds, or breed carrier to carrier. Briards are required to be solid
colour - the French Breed Standard heavily penalising any white markings or signs of depigmentation but it
does allow blacks to have scattered white hairs through the coat. Usually, when original dog breed standards
vehemently disapprove of white in specific ways, it is with just cause, e.g. Boxer, Dalmation, Border Collie,
etc. suffering organ failure. The Briard has been used to found other breeds and, again, the anti-white
stipulation has carried over to them too. I would hasten to add that many dog breeds allow, and favour,
white but obviously no lethals or birth disabilities are associated with these types, e.g. Samoyed, West
Highland White Terrier, Poodle, etc.
Another version of ApW could be extended snowcap with a low percentage of spots, either large or small, to
the white. Not always getting colour but, nonetheless, a relatively high colour producer around the 80%
mark. Other mostly white horses would also be good colour producers.
-7-
Lower Colour Producers
Other appaloosa markings could be represented by Apw:
Apwlp
Apwsb
Apwsf
Apwfr
Apwmo
Leopard
Spotted Blanket
Snowflake
Frost
Mottled
perhaps in this order of dominance, but not necessarily so as certain Leopards and Spotted Blankets could
alternate. These markings are seldom claimed to be high colour producers hence their lower case. The
chances of each being found in homozygous form is slight because the interbreeding of all the markings,
together with regular crossbreeding with other breeds, would heavily favour the heterozygous state. In any
event, it is not clear-cut in visually defining one marking from another, e.g. at what point does an extended
Spotted Blanket become a Near Leopard, that could also be the description of a Spotted Blanket that has
‘roaned.’ However, clear and evenly marked individuals of similar singular pattern would be the easiest for
selective homozygous breeding, ‘full’ leopards for example.
When sabino moves from minimal expression to moderate (e.g. bald face/chin spot/stockings) in the
presence of appaloosa markings, it appears to suppress the coat spots of appaloosa but, curiously, often
seems to act like a magnet for varnish/’roan’/marble and frost markings. It could be therefore, that sabino
ticking (which is believed to be inherited recessively), when present, encourages these ‘lesser’ appaloosa
markings with the possibility of both appearing together in some individuals, although this would be
difficult to determine phenotypically.
As an example, the 1940s saw Appaloosas appearing from recognised Quarter Horse lineage, some
obtaining dual registration. In the early 50s a dun with large white blanket across the loins, broad blaze,
chin spot and stockings emerged via a line of sabino/splashed white ‘roans’ in an otherwise solid pedigree
(taking his dun dilution from the solid sire) and was registered as an Appaloosa. The cream dilute dam
showed considerable sabino/splashed white markings, including blue eyes. Four generations back through
the dam saw a palomino sabino Quarter Horse bred to an Appaloosa crossbred, resulting in ‘roan’ and
considered Quarter Horse. From this mating sabino and cream would also have been inherited with both,
plus the ‘roan,’ carried down for two generations to the blanket’s dam (despite further crossbreedings to
solids along the way). From this same dam, a bay solid filly born four years earlier had already expressed
her sabino/splashed white potential via one blue eye, white chin spot, blaze and feet, and was registered as a
Quarter Horse. A female chestnut ‘roan’ cousin from the same sabino/splashed white ‘roan’ line, but not
exhibiting sabino/splashed white herself, was dual registered and when bred to the blanket allowed moderate
sabino and frosted hips by way of red dun, taking Appaloosa registry.
(Splashed White is a spotting pattern where white appears horizontally across the bottom half of the body
and tail, with bald face and blue eyes.)
Composites
As more than one appaloosa marking can be found on the same horse, it is logical that any combination of
markings is possible which, in turn, would give a better chance of passing colour to the next generation but
obviously lessening homozygosis of a particular marking. What about small base colour flecks all over a
white body, similar to the flea-bitten grey? Could this be an extreme Snowflake, maybe a homozygous
Snowflake, or could it be a Leopard influenced by extensive ticking of some kind? What about the white
horse with both flecks and rump spots? Is it a Snowflake and Spotted Blanket or a ticked Leopard and
Spotted Blanket, or is there a concentrated re-pigmentation affect at work, melanins (pigments) not always
stabilised at birth.
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Potential Range
ApWApW
ApWApw
ApWS
(ApwApW
ApwApw
ApwS
SApw
(SApW
SS
ApNS
ApNApW
ApNApw
(ApNApN
(Few Spot) or Snowcap, true
Few Spot or Snowcap, carrying ‘other’ markings
Few Spot or Snowcap, carrying Solid
‘Other’ markings, carrying any Few Spot components or Snowcap)
‘Other’ markings, true
‘Other’ markings, carrying Solid
Solid, carrying ‘other’ markings
Solid, carrying any Few Spot components or Snowcap)
Solid, true - non-Appaloosa
Non-characteristic, carrying Solid
Non-characteristic purebred, carrying any Few Spot components or Snowcap
Non-characteristic purebred, carrying ‘other’ markings.
Non-characteristic purebred, true (carrying appaloosa markings)
Those in brackets would be rare. The ApW (high white producing Appaloosa) is highly dominant over S
(Solid non-Appaloosa) in the ApWF and ApWSC forms (perhaps 95% or more for heterozygotes, 100% for
homozygotes); the Apw (lower white producing Appaloosa) much less so. ApN dominates all appaloosa
markings.
White Overlay
There appears to be five types of white overlaying effects seen in the Appaloosa. One is Grey, which is
introduced by crossbreeding to a grey individual of another breed. Grey is inherited dominantly and
progresses as a horse ages to eventually give all-over white, obliterating the base colour and any coat
markings. It therefore serves no purpose to introduce it to any breeding where coat markings are desired. A
grey horse will always have at least one grey parent, and has a 50% chance of passing grey to offspring if it
is heterozygous for grey, or 100% if homozygous.
Another white overlay effect is the Appaloosa displaying sabino pattern. If the horse does not exhibit any
other appaloosa characteristics, it may be that the overlay is the ticking associated with sabino and the horse
is primarily a Solid. In addition to ticking, sabino is also capable of exhibiting minimum snowflake. Some
Frost and Snowflake Appaloosas may therefore be questionable.
The third white overlay effect is the Appaloosa displaying Coon Tailed Ticking (rabicano). This type of
ticking is always associated with horizontal bands of white hairs at the tail root, this ‘brush-tail’ being the
only indication in some individuals. Accompanying ticking can appear at maturity and sometimes at birth.
Ticking, if present, is most concentrated in the flank and lower body areas. Rabicano is believed to be
inherited recessively. As with the sabino pattern, if the horse does not exhibit any other Appaloosa
characteristics, it may be that the overlay is the ticking associated with rabicano and the horse is primarily a
Solid. Rabicano and sabino can appear together in the same individual.
The fourth white overlay effect is Varnish/’Roan’/Marble - a progressive overlaying of white - exclusive to
the Appaloosa and believed by some to be inherited as a separate but associated gene of a dominant nature V
as it can appear on its own, or lays over other markings but not necessarily to their exclusion. Presumably it
is not inherited by an homozygous SS of Appaloosa ancestry, but could it be available to an ApN-?
Thoughts are that in homozygous form VV, varnish fully extends the overlay thickly over most of the body
leaving base colour on prominent bones, termed as ‘Varnish Roan.’
The typical varnish onset age is 2-6 years but some foals varnish quickly from birth. Those individuals
without other coat markings would be Mottleds who also exhibit the varnish gene. If neither parent
varnished to any degree, then a different gene would be involved. It is important to remember that, without
other characteristics, the overlay could be a ticking gene and not the Appaloosa varnish gene.
-9-
Although it may have its origins in the roan of other breeds, varnish is not considered lethal in any way as
can be that marking in homozygous form. Roans of other breeds are born so and do not change, with heads,
lower legs, mane and tail of base colour. Dominant genuine roan could also exist in today’s Appaloosa, via
non-Appaloosa ancestors.
Roan, ticking and varnish may be linked.
There is also the ‘fading’ during foal shed of some individuals born Near Leopard or extended Snowcap –
the receding of the solid areas of base colour, leaving spots or just white. This may not be the varnish gene
but a natural initial protection of extremities, keeping broken skin pigment to a minimum; the melanins
stabilizing after birth. Dog breeds of the far north are commonly born with facemasks that fade in the first
year, allowing nose, lip and eye rims more chance of protective pigmentation.
Genetic Patterns
Thus there would be three genetic patterns forming the basis for the many accepted markings found within
the Appaloosa Breed:
ApW
Apw
-V
High colour producing Appaloosa (Few Spot and Snowcap)
Lower colour producing Appaloosa (Mottled, Frost, Snowflake, Spotted Blanket
and Leopard)
Varnish Appaloosa
and possibly eight types of Solid found within the first generation of an Appaloosa Breeding:
SS
SApW
SApw
SApN
ApNS
ApNApW
ApNApw
ApNApN
True Solid, carrying no spotting at all
Solid, carrying any Few Spot components or Snowcap
Solid, carrying ‘other’ markings
Solid, carrying Non-characteristic
Non-characteristic, carrying Solid
Non-characteristic purebred, carrying any Few Spot components or Snowcap
Non-characteristic purebred, carrying ‘other’ markings
True Non-characteristic purebred, carrying appaloosa markings
ApNApN would be rare, in so much that identical genetic base colour Non-characteristics would need to be
bred together for it to occur.
Accuracy
Foal markings are crucial in defining accurate markings, both at birth and at coat sheddings, with parent and
sibling history helping to clarify indecision. Later, their offspring can also lend further definition.
It is also important to record the base colour of the individual, i.e. Bay, Brown, Black or Chestnut; any dun
dilution, i.e. yellow, mouse, grullo/a, red; any cream dilution, i.e. buckskin, palomino; and any double cream
dilution, i.e. perlino, smokey perlino, cremello. Sabino markings should also be recorded, as too any signs
of varnishing.
Eventually, DNA will be as detailed to identify the minor white modifying genes as well as the main Breed
gene itself, to remove all doubt. But, until that time, breeders of today - the current caretakers of the Breed should endeavour to declare base colour and markings on pedigrees and support with photos, to allow those
following to find their way in perpetuating Appaloosa colour.
© Lynn Harrison, May 2006