Chetar Arabians ~ EQUINE COLOUR GENETICS ~ Sabino Overo ~

Sabino Overo is a Polygenic Incomplete Recessive white spotting pattern gene with the widest range of marking manifestations of all of the white pattern genes. Sabino Overo predominantly manifests in highly irregular sollid white markings, and in addition can cause minimal to extreme enitre body coverage of white that manifests in a ticking [ie. roaning] type of pattern. A Sabino Overo patterned horse will always have lip and/or chin facial white in conjunction with leg white. Though both can occur in the most minimal of forms - ie. A small five cent piece size lip/chin spot along with a single white coronet band - Both of these Sabino Overo characteristics must be present for a horse to be classified as phenotypically Sabino Overo.

During the past decade Sabino Overo became the subject of targetted research due to a huge increase in popularity of the pattern. A single massive development as a result of this research was the identification of the Sabino1 Gene, the Sabino Overo gene present in Paint/Quarter Horses and their derivatives [including many Pintos] and for which there is now a DNA Confirmation Test for, with this targetted research also confirming the existence of more than one Sabino Overo gene in general. There is undoubtedly at least two, with the Purebred Arabian so far proven to be at least one source breed of the second, though as yet this secondary Sabino Overo gene remains unmapped. Further unconfirmed Sabino Overo theories include the presence of a third Sabino Overo Gene, with this possibly being the singular cause of all leg and facial white markings, and so existing in all, or possibly bar only a few, breeds.

For the purpose of this page, the information contained herein is in regards to the white spotting pattern markings caused by the Sabino Overo gene[s] and does not refer to the commonplace, limited white facial and leg markings that may or may not be the result of a separate subtype Sabino Overo Gene. Anyone who has visited the Chetar Arabians website before would likely have noticed my preoccupation with the Sabino Overo pattern - Every single one of Chetar Arabians coloured horses, both Purebred and Derivative Arabian bred, all express the Sabino Overo pattern as a minimum, with all bar a couple carrying additional colour gene expressions in addition to their Sabino Overo. Sabino Overo is by far my favourite of all white pattern genes, and the one I have the most interest in researching as a result.

The Sabino Overo Gene can cause a wide variety of marking manifestations, and is widely recognized as being the most difficult to predict of all coat colours. There are two Primary Coat Markers for the Sabino Overo Gene. While the variety of markings is extensive, the two Primary Coat Markers for Sabino Overo remain the same across the board, regardless of the possible Sabino Overo subtypes possibly present.
These two Sabino Overo Primary Markers are a white facial marking in conjunction with white leg marking[s].
Specifically, an upper and/or lower lip and/or chin marking with underlying pink skin, in conjunction with at least one white leg marking with underlying pink skin as the absolute minimum indicators for Sabino Overo. In order for a horse to be classified as Sabino Overo, it must have a lower facial marking combined with a lower leg markings as the minimum, with or without additional, Secondary Coat Markers dependant upon the expression classification.

Please note that as white facial and leg markings are very much commonplace throughout all breeds regardless of whether a horse carries Sabino Overo or not, there are specific marking characteristics that are recognized as being Sabino Overo indicators. These characteristics apply to both the Primary and Secondary Coat Markers and are detailed below in the Sabino Overo Marking Characteristics. There is a distinguishable difference between commonplace facial markings and those that are the result of the Sabino Overo Gene.

White Ticking is one of the more common Secondary Coat Markers of the Sabino Overo Gene. The White Ticking can manifest anywhere on the body, though most commonly appears at the lower flank area initially, radiating up and out from this area. Sabino Overo White Ticking can be as little as a few white hairs at the flank, through to an extensive coverage of intermittent white hairs that covers the entire body of the horse. The Sabino Overo White Ticking trait can appear with any expression of the gene, though the appearance of the White Ticking as the only Secondary Sabino Overo Coat Marker usually indicates a Minimal Expression of the gene, while the appearance of further Secondary Markers along with the White Ticking is indicative of a more intense expression.
It should be noted that White Ticking can be a manifestion resulting from the one, or both, of the White Roaning Genes, Rabicano and/or True Roan. As a result, the cause of White Ticking can easily be misidentified. There are, however, Primary Coat Markers of Rabicano & True Roan that enable correct identification of the gene at work - See the RABICANO &/or TRUE ROAN pages for more information on identifying these genes.

This theory is quickly becoming the foremost of the three, with mounds of evidence pointing towards it both historically as well as presently as huge leaps are made in the mapping of equine colour genes. The most recent advance in this area has been the discovery and identification of the Sabino1 Gene. This gene has been confirmed to be present, and prevalent, in the Paint Horse and the Pinto types derived from it, whilst also been proven not to exist in the Arabian breed and its' derivatives [that aren't a crossbred Paint Derivative as well]. Which all lends support to this final theory on the Sabino Overo pattern.

This theory is that there are multiple subtypes of the Sabino Overo Gene, with these controlling A) General White Markings, B) Restricted [Minimal] Sabino Overo Markings and C) Extensive Sabino Overo Markings. It is theorized that the first two are polygenic and the latter is single-dominant in inheritance and so is essentially a generalized theory that is supported by the evidence of both the Sabino Overo theories as well as one of the theories of behind the regular white markings seen on many horses across most breeds. The Sabino Overo Gene having multiple subtypes, or even completely separate genetic mechanisms actually makes much more sense when all of the evidence is considered. There are too many contrindications with each of the two theories noted above for either to be the be all and end all of the Sabino Overo pattern.

This is the general term applied to one of the foremost indicators of the Sabino Overo Gene. Edges classified as "Regular" are those wof smooth, rounded edges with crisp, clean border lines between the white marking[s] and the background colour. Anything not classed as having a regular edge is considered to be an irregular edged marking. Broadly speaking, the Sabino Overo Gene causes Irregular Edged Markings, while all of the other white spotting pattern genes, Tobiano, Frame Overo and Splashed White Overo, all cause Regular Edged Markings [in that order of intensity].
The more common Irregular Edged markings are often described as 'Jagged' and/or 'Pointy' edged solid white markings.
The Jagged/Pointy edges usually appear on the leg and sometimes the facial and head white markings, but can also apply to any or even all of the body markings. The edges falling into the Jagged/Pointy classification can be subtle 'quiet' edged markings reminiscent of, and sometimes termed, sharks teeth that can easily be misidentified, right through to the 'loud' edged markings that have very distinct and harsh angle changes almost impossible to miss or incorrectly identify regardless of the distance at which they are viewed. While the former will generally be an equally edged marking that requires close inspection to correctly identify, the latter will easily be seen to have distinct changes in direction and coverage, such as a leg marking that terminates at the fetlock in front and the knee in the back [or vice versa], or a lopsided facial marking extending over the jaw on one side and not the other side of the head.

There are many more horses than people generally realize that carry the Sabino Overo Gene in its' more minimal expression. For example, most Tobiano horses carry the Sabino Overo Gene [or if not Sabino Overo another white pattern gene], with true Tobianos - ie. horses expressing Tobiano only - actually being extremely rare [See Sabino Overo in Combination with Other Genes below]. There are almost always subtle differences in the markings of all horses carrying the Sabino Overo Gene that allow for identification of a horse carrying Sabino Overo Gene in addition to another white pattern.

Throughout this site I have used the terms Primary Coat Markers and Secondary Coat Markers in an effort to simplify the task of identifying the individual genes and resulting patterns caused by them. Primary Coat Markers are the markings and/or characteristics that a horse MUST POSSESS to be classified as carrying a specific gene, while Secondary Coat Markers are the markings & characteristics that a horse MAY or MAY NOT possess, that are used to further classify the degree of pattern expression caused by the specific gene. Furthermore, I have outlined the various markings attributed to individual genes individually, and split them into two groups - The frist identifies the markings that are attributed to being caused by a single, specific gene alone, and the second group identifies the markings that could result from that specific gene but are also attributed characteristics of another gene as well.
The TERMINOLOGY PAGE contains full explanations of the more uncommon and/or technical terms I've used throughout this site.

As previously mentioned, the Sabino Overo Gene can manifest in an extensive variety of markings, with solid patches of white markings being one of the more common manifestations. Sabino Overo can cause solid white patches to appear anywhere on the body, though the more common areas of appearance are along the ventral areas of the horse [in addition to the Primary Coat Markers of facial and leg white]. Specifically, the underside and along the jawline, the throatlatch, the belly and underside of the flank regions, and often between the hind legs as well.
These trait characteristics though, while common to the Sabino Overo Gene, can also be seen in some individuals carrying the other Overo genes as well as the Tobiano Gene. Sabino Overo commonly occurs in combination with any, and rarely all, of these ofther white spotting pattern genes as well, so the section below on Sabino Overo Marking Characteristics should be used to identify solid white patches that can be attributed as being caused by, or affected by, the Sabino Overo Gene.

The solid white markings appearing on the body that are caused by Tobiano and the other Overo Genes [generally] always have clean, crisp edges. Those that are a direct result of the Sabino Overo Gene, or that are affected by the Sabino Overo Gene when it appears in concert with one or more of the other white spotting pattern genes, are not clean nor crisp in any way. As also previously noted, the Sabino Overo Gene can cause large amounts of white ticking, and it is a variation on this trait that differentiates Sabino Overo caused and/or affected solid white markings. The edges of the solid white markings appear to "bleed" or "leak" into the background colour, hence the term used to identify the trait. The characteristic is actually an interspersal of white and background coloured hairs where the white and background colours meet. The white marking edges, rather than being crisp and clean, have white ticking shadowing the solid white, producing the effect of the white pattern having "bled", or "leaked" into the background colour of the horse.

This is a further descriptive term given to specific Irregular Edged markings that most often occur on the legs and head, but are also seen on the body markings of some individuals. The term is used to describe all of the white markings with the specific appearance, but are most commonly used to describe the unusual leg markings that are a gene specific trait of Sabino Overos. Lightning Strikes are solid white markings that form narrow strips of white. The edges of lightning strikes carry the same distinctive Sabino Overo characteristic of being highly irregular [as described above].
On the legs they travel vertically up the leg, in a narrow and spear like pattern, and gradually taper off to terminate in a narrow point. The leg lightning strikes are usually seen on the front of the rear legs [this is the most common area of manifestation] and on the rear of the forelegs. They may be disconnected from other solid white leg markings or connected to white leg markings. When connected, it will appear that the horse has a usual, even lower leg marking that terminates as usual most of the way around the leg, with only a small area of white continuing to spear up the leg, giving the connected white marking harsh angle where the lightning strike continues up the leg.
On the head, lightning strikes appear on the underside of the jaw, in some cases extending over the underside of the jawline, possibly as far as to join with white markings on the face [ie. to a blaze or apron face marking], though this is rare. Where the leg lightning stirkes travel in the direction of coronet to stifle [though may not extend that entire distance], the head/jaw lightning strikes travel from the area of the throatlatch towards the chin. Much the same as with the leg lightning strikes, they may be connected to a white marking at the throatlatch area before extending up the jaw in a harsh, angular pattern, or they may be completely disconnected from any other white at the throatlatch. It is common for these markings to coincide with a lightning strike marking at the throatlatch and/or upper neck area, though this is not a mandatory trait. The throatlatch/upper neck lightning strikes are usually much shorter, and usually thicker - still narrow and angular, but not as thin as the leg and head lightning strikes, and still terminate in a sharp point if they're not connected to the head lightning strike.
As mentioned, lightning strikes may also occur on the body of some individuals. The most common body lightning strikes are found on the belly. It should be noted though, that body lightning strikes are much less intense than those that occur on the head and legs. They are usually smaller and much shorter than those of the head and legs, and aren't usually as irregular in appearance either. They can easily be mistaken for, or confused with, some marking manifestations cause by the Tobiano Gene and other Overo Genes and as such should not be used as a main indicator or identifier for the Sabino Overo Gene.

Minimal Sabino Overos express the two Primary Coat Markers of a facial white marking from a small lip and/or chin snip, up to a connected small star, thin stripe and snip to upper/lower lip and chin, along with one or two at the most, white leg markings. The leg markings will not extend past the half cannon area. Minimal Sabino Overos may also possibly possess some minimal white ticking at the flank and/or belly areas - A light 'sprinkling' of white ticking only in thes regions, along with the minimal facial and leg markings as decribed above, is indicative of a Minimally Expressed Sabino Overo.
This is the most common expression of Sabino Overo, and also the one that is easily missed and classified as general, commoplace facial and leg white.

Moderate Sabino Overos have a facial white marking from large star, reasonably large connected strip covering part of one nostril to lip and/or chin through to a wide blaze covering both nostrils, full lips to terminate at the chin.
They have two or more white leg markings. If they have only two leg markings they will usually extend to the upper cannon through to knee and/or hock areas, and usually have at least one highly irregular termination shape to the leg markings through to complete lightning strikes. If they have more than two leg markings they will be irregular edged and at least one will extend into the cannon region.
Moderate Sabino Overos will usually possess quite an extensive array of white ticking radiating out from the flank area, possibly across the entire body.
A more intensively marked Moderate Sabino Overo will also have one or more small belly splashes and/or patches measuring more than 4inches that may possibly extend or be that numerous as to cover up to 50% of the body [so the horse is 50/50 white and background colour].

Maximum Sabino Overos have an extensive facial marking, a wide blaze extending to the eyes at the side, and covering the entire lower head to the entire chin [bald face] through to an entirely white, or nearly so, head [including under and along the jaw to throatlatch]. Maximum Sabino Overo have four white leg markings that all extend up over the knee, or that are disconnected over the knee [and so have multiple markings on the one, or more, legs] and extend up to completely or partially cover the forearm to shoulder and gaskin to stifle. The body of Maximum Sabinos will have solid white patches and/or white ticking so intensive that there is more white on the body than there is the background colour of the horse. Moderate Sabino Overos may also have one or both eyes parti coloured and/or blue as a result of the Sabino Overo Gene. This will happen if the white facial marking travels through or over the eye area/s.

The term Extreme Sabino Overo is usually reserved for those indiviudals that are 85% to 100% white in colour. The white may be the result of solid white patches or intensive white ticking, or as in most cases, a combination of both. Even though these individuals are technically background coloured horses with the Sabino Overo Gene markings superimposed upon the background, these individuals are so white in colour that they will appear to be the reverse - white horses with a sprinkling of background coloured hairs in limited areas, through to a completely white horse with not one hair of background colour. Extreme Sabino Overos will also have completely blue eyes. Extreme Sabino Overos are very rare and valuable. They are also theorized and widely accepted as the Homozygous form of [one of] the Sabino Overo Genes, and/or possibly the result of a combination of multiple Sabino Overo Genes.

A very common misconception in regards to Sabino Overo is that of the facial and leg markings. It is commonly believed that for a horse to be classified as Sabino Overo, even in its' most minimal expression, an individual must possess facial and leg markings that can easily be distinguished from the regular, normal facial and leg markings that most individuals in most breeds have, when this is simply not correct. An individual needs only to have a small lower head marking, like a snip, that covers only a small area of the upper and/or lower lip and/or chin, in conjunction with a small, from coronet to pastern, leg marking to indicate and possibly possess the Sabino Overo Gene. They must have these to be Sabino Overo, but they only need as much white as this as well. The white facial and leg markings of Sabino Overos though, do have disguishable characteristics that allow for easy identification when you know what to look for - See the Primary Coat Markers and Marking Characteristics above for more information on just how to identify if a horse carries Sabino Overo.

Due to the very similar patterns of white ticking that can result from the Sabino Overo & Rabicano Genes, these two genes are often mistaken for one another. They do, however, have some very distinct difference that can be used to differentiate between the two separate pattern genes. The Primary & Secondary Coat Markings and Marking Characteristics section on this page, the section directly below on Sabino Overo vs True Roan, and the RABICANO page also for detailed information on these differences and how to identify which gene is present.
It should be noted that it is very common for both the Sabino Overo Gene & the Rabicano Gene to occur in conjunction with each other to varying degrees of expression and so particular attention needs to be paid to coat markings that can rule out or rule in either and/or both Sabino Overo &/or Rabicano.

True Roan is the only gene other than Sabino Overo & Rabicano that is attributed to manifesting in white ticking. While Rabicano is limited in the areas of where the white ticking will manifest, Sabino Overo is not & so this makes for easier distingushing markings between the two. True Roan, however, is much less limited in marking manifestations that Rabicano, and so it can be much harder to distinguish from Sabino Overo. There are a number of tell tale signs though, and these can rule out True Roan, as well as Rabicano in some cases, and leave Sabino Overo as the only possible, exclusive causative.
For example, the main distinguishing characteristic involves the head. Sabino Overo may cause white ticking on the head. True Roan will not under any circumstances produce white ticking forward of the area from poll to throatlatch - No white forward of this line is one of the Primary Coat Markers for True Roan. So if white ticking appears on the head you can be guaranteed that True Roan is not the causative. Rabicano also rarely manifests in white ticking on the head so in circumstances where there are no other firm Rabicano indicators, it can also be ruled out [See RABICANO page for more information].
Sabino Overo is also present in most breeds, however True Roan is not. For example, the Arabian breed does not have True Roan but does have Sabino Overo as well as Rabicano, with these being quite prevalent in a number of the breeds' families.
There are more traits such as these examples, that are unique to the True Roan Gene to look out for, which are dealt with on the TRUE ROAN page.

The three Overo Genes have many misconceptions surrounding them due to past tendancies to lump them all under the same name. Even though they are all Overo Genes, each is a result of of very separate genetic controls. The nonclemanture of the Overo Genes has resulted in the common misconception that the fatal genetic mutation known as Overo Lethal White Syndrome can result from all three of the Over Genes. Over Lethal White Syndrome has a 25% chance of occurring when two horses carrying the Frame Overo Gene are bred. Overo Lethal White Syndrome causes an in utero foal to not completely develop and subsequently be born with an incomplete digestive tract that results in death, usually within 24hours of birth. OLWS is a genetic mutation that only occurs in Homozygous Frame Overo horses - ie. individuals that inherit two dominant Frame Overo alleles from their parents.
This misconception has been further enforced by the fact that all Homozygous Frame Overos are completely white, much the same as an Extreme Sabino Overo is, leading to the belief that breeding two Sabino Overos also has a one in four chance of producing progeny that will inevitably die within hours of birth. Sabino Overo has absolutely nothing to do with OLWS, and neither does Splashed White Overo - OLWS results only from the Frame Overo Gene.

The Sabino Overo Gene can appear in conjunction with any white pattern as well as on any background colour.
The most common combination is of Sabino Overo appearing with Rabicano, and it is in fact theorized that these two genes may be linked [see Genes & Markings Linked to the Sabino Overo Gene below]. When the two of these genes appear together, the result can be quite striking, with the horse usually displaying generous amounts of white, with both solid white markings as well as white ticking. Sabino Overo and Rabicano are most commonly seen together when both are in their minimal expressions, with these still amounting to quite a lot of white. There are a number of individuals with moderate to maximum expressions of both genes, though this is considered rarer than the minimal expression combination.

Sabino Overo is another of the least researched of all equine colours. There are innumerable theories surrounding this Gene and the subsequent variation in patterns that it produces. Depending upon personal experience and the geneticists prefferred, just about everyone lends their support to a single theory.
As previously mentioned, there are numerous names and classification definitions for this pattern only somewhat dependant upon locality. However, the term "Sabino" even though this is not technically a descriptive term for this pattern, has surged in popularity as the definitive name for the pattern/gene. As Sabino is now known to be one of three patterns historically known [and still termed by South Americans] as having been lumped under the one name "Overo", the official pattern name generated at this locus is "Sabino Overo".

There are three main theories surrounding the genetic control of the Sabino Overo pattern. Each has its' own supporting evidence, and its' own supporters.
The first theory suggests that Sabino Overo is the result of polygenic factors, while the second is supportive of a single allele locus as the genetic control. The third theory essentially incorporates both of the above theories, and is based upon there possibly being multiple subtypes of the Sabino Overo gene.

Remembering that Sabino Overo can manifest in as little as a small facial marking in conjunction with a small leg marking, it is only logical to assume that there are many individuals worldwide that are in fact Sabino Overos yet have been classified as having 'regular/normal' white markings only, lending further support to the current evidence surrounding the theory of Sabino Overo, or a Sabino Overo subtype, being the source of all white markings.

It is widely recognized that all white markings, from regular facial and leg white right through to all white spotting patterns, are always more prevalent on chestnuts than bays, and in turn more extensive on bays than blacks. Furthermore, a Bay that carries the genetics to produce Chestnut [Ee, AA] will have more extensive white markings, and be able to produce more extensive white markings, than a Bay without the Chestnut genetics [EE, AA]. A similar relationship between white markings and patterns to Base Colour exists with Blacks based individuals, with Blacks carrying a recessive extension allele [Ee, aa] is more reliably going to possess and in turn produce more extensive white markings than a black without the recessive extension allele [EE, aa].
These relationships point to a genetic linkage of all white patterns and markings to the Base Colour of the horse.

While there are multiple theories on the genetic control of the Sabino Overo pattern, there is data that all supporters of the multiple theories generally agree upon - That the Sabino Overo pattern requires a specific balance between other loci to be expressed phenotypically.

There is some evidence that the Sabino Overo Gene, or at least one of them, is linked to the Rabicano Gene. It is very common for both genes to be phenotypically expressed on a single horse - It is much more common to see a Rabicano that also displays Sabino Overo characteristics than it is to see a Rabicano with no other pattern gene. It is also common enough that many people mistake their Minimal Expression Sabino Overos as Rabicano, as the Sabino Overo Gene in its' minimal expression predominantly manifests as white ticking in a pattern that can clearly resemble that of the Rabicano Gene. The trick to identifying which horse/s are Sabino Overo or Rabicano or a combination of both is to further assess the horse for each of the individual Primary Coat Markers mentioned above on this page for the Sabino Overo Gene and at the top of the RABICANO GENE Page. The presence of the Primary Coat Markers for each of the genes usually always assists with the clear identification of which pattern is, or if both patterns are, responsible for the white ticking.

The possibility of a genetic linkage between the Sabino Overo Gene [or one of them] and the Tobiano Gene has a lot more supporting evidence than many people realize. It is not commonly known that the Tobiano Gene occurring alone with no other white pattern present is extremely rare, and that the most common pattern to occur along with Tobiano is Sabino Overo. Think about how many Tobiano horses you have seen throughout your life - Now just how many of those Tobianos have a completely solid, dark/base coloured head with no white forward of the poll to throatlatch? I bet it's not many! Just about every Tobiano horse has a white facial marking of some kind, and all of those are either Minimally Expressed Sabino Overos and/or have Regular White Facial Markings. Once again, the trick to distinguishing between the two is to further assess the white markings seen on the horse for the Sabino Overo Marking Characteristics noted above.

And then there is a theory not limited to just the Sabino Overo, though it could possibly account for all of the problems seen with the Sabino Overo theories.
There are many obviously, loud marked Sabino Overos that have very plainly marked parents. These Sabino Overos are real Crop Outs, that go on to reliably produce extensively marked progeny themselves. The problem is that the genetic control of these Sabino Overos cannot be explained by either the polygenic theory nor by the single-dominant theory. So, the result is that we also have a theory of an additional allele or completely separate gene linked to the Sabino Overo Gene, that contains an instruction to 'mask' the Sabino Overo expression. One of the terms given to this theorized gene is the "No White Gene". This gene may or may not also be responsible for the completely solid coloured horses that have no white markings whatsoever, or at the very least those horses in this group that consistently produce no white markings in their progeny [there are many families recognized for this trait also].
This additional gene could possibly be responsible for the not only the Crop Out individuals noted in the second theory, but could also explain the variations in how extensively marked individuals and their progeny are within the families supporting the first theory in addition.

There are those that takes this third theory one step further, claiming that this theorized "No White Gene" is an incomplete recessive carried by all horses. That in Homozygous Recessive there is no instruction and the gene has no affect on genotype and the horse expresses the full white marking genotype instructions comprised by other gene loci - This allele combination would account for the moderate to loud expressions we see across the white patterns.
In Heterozygous form there is an instruction of "Restrict White Markings" and the horse expresses limited white facial and leg markings - This allele combination would account for the "regular" white facial and leg markings we commonly see across most breeds.
In Homozygous Dominant form the instruction is "No White Markings" - This allele combination would account for those few horses that do not have any white markings at all.
This gene is theorized to be a "further instruction" to those contained within the individual white pattern gene loci, and so does not account for the actual pattern we eventually see, only if and how much of the pattern we do see. This theory could explain data collected in both theories for the Sabino Overo Gene, and could also support some evidence of the Sabino Overo subtype theory as well.

In contrast to the polygenic theory, there is evidence that in some families of horses, the Sabino Overo pattern seems to be inherited in a way that indicates a genetic control of a single allele, and in most cases, these inheritances point to that single allele being dominant, as opposed to the recessive polygenic inheritance theory noted above. Individuals of these families are usually moderately to loudly marked in expression themselves, and consistently produce a high percentage of moderately to loudly marked progeny. When bred to another horse possessing minimal or more intensive Sabino Overo indicative markings, there seems to be an almost 100% chance of at least minimal Sabino Overo inheritance in their progeny.

There is a lot of data that supports a trend of some families to produce the Sabino Overo pattern in their progeny more reliably. Individuals of these families may or may not have extensive white markings themselves and yet are able to and will produce loudly marked progeny themselves, in some cases irrelevant of the markings of the other parent. This is consistent with a recessive polygenic mode of inheritance. This theory essentially suggests that the mating of one of the Sabino Overos of these recognized family lines will consistently produce foal crops with the pattern regardless of the phenotype of the other parent.

White Ticking is a proven pattern trait of [at least] two other white pattern genes, those being Rabicano and True Roan. As such, it can be difficult at times to distinguish between the three and there are many commonplace mistakes made with the identification horses that carry one or more of these genes.
While they all can manifest in white ticking, each has its' own specific pattern of manifestation, and the differences in there is what is used to distinguish each pattern individually and in combination with eachother.
The more important rule to remember when trying to identify Sabino Overo as a white ticking pattern causative is that Sabino Overo results in areas of white ticking that are generally even across the entire body regardless of intensity and the white ticking will always appear in conjunction with at least one white leg marking and a white facial marking that extends to lower lip and/or chin area.

The basic principles I use when first approaching the separate identification of these three patterns are the following two, very simple rules:
1) Does the horse have white ticking in areas other than the dock/tail and flank? If not, it is Rabicano. If so, it's not Rabicano; move on to step 2..
2) Does the horse have white ticking anywhere on its' head? If so [& it also have white facial & leg markings], it's Sabino Overo. If not, it's Roan.
It should be noted through, that the rules stated above are only the first steps to identifying each of the patterns in general and that further additional steps of assessment may need to be taken in some cases dependant upon the intensity of expressions, so above rules do not always apply in all cases.

There are a number of other genes that manifest in white spotting patterns. While there are rare occasions when it can be almost impossible to predict a horses' genotype simply by assessing the phenotype [this can be a common occurrence with horses that are, or almost are, completely white with no to minimal dark/base coloured pigmentation], these instances are few and far between. There are some very identifiable differences between each of the colour genes that generate patterns of white suerimposed upon a dark/base colour. These simple differences are discussed on the WHITE PATTERNS INTRO Page.

As Sabino Overo has never been the subject of formal studies, the controlling loci and recessive vs dominant vs wild alleleic combinations present at the gene are still unknown, so the following abbreviations are really just 'guesses' by those in the know at the genetic control and the alleles that lie there are.
Sabino Overo is represented by the locus abbreviation [Sb].
A horse that does not carry Sabino Overo is [SbnsSbns] at the Sabino Overo Locus.
Non Sabino Overo/Heterozygous Recessive = [SbnsSbns]
Heterozygous Sabino Overo = [Sb+Sbns]
Homozygous Sabino Overo = [Sb+Sb+]

Note: With the true genetic mechanisms of Sabino Overo being questionable, a horse being Homozygous for Sabino Overo remains unable to be absolutely confirmed. As such, rather than claim homozygosity at the Sabino Oveo allele that cannot be definite until such times as official research is conducted, "second Sabino Overo locus allele unidentifiable" [ie. possibly homozygous], is technically the correct method of abbreviation. This representation being a dash/subtraction symbol = [Sb-].
Also, a non-Sabino Overo ie. Homozygous Recessive Sabino Overo will usually not have the recessive alleles depicted in the genotype, so if there is no Sabino Overo in a genotype, it is safe to assume the horse is [considered to be] Homozygous Recessive at the Sabino Overo Locus and as such is not Sabino Overo.