Breed Information
Colour Coat Genetics - Grullo
  

WHAT DOES A GRULLO LOOK LIKE?
The body of the GRULLO (pronounced GREW yo or GREW ya) will typically appear gray, silvery, smoky, or some lighter or darker version of these colours. Each of the hairs on the body is silvery or smoky –it is not a mixture of white and black or dark brown. AQHA oftentimes uses the term 'mouse- coloured.' One may note that a wild mouse is smoky-gray in colour. Some GRULLOS may have a 'warmer' hue to their coat whereby the coat has a ‘tannish' hue, somewhat similar to that of the DUN. Some terms in independent texts on horse colours will give exotic sounding names to some of the variations the GRULLO, such as 'olive grullo' or 'lilac grullo.' In any event the basic characteristics are the same; the body colour as described above, black points with black DUN characteristics-dorsal stripe, zebra stripes on the legs, stripes over the withers-and a black or very dark brown head. And it is this solid black or dark brown head that is one of the distinguishing characteristics one finds on the GRULLO. The head on the DUN is typically the same or similar to  the rest of the body colour.

The GRULLO is not a common colour in the Quarter Horse, yet it is often confused with other coat colours. Some DUNS may have darker hair covering their body to some degree. This is due to the 'smutty' or 'sooty' gene and may affect the face and back. The 'smuttiness' affecting the face will often give the DUN 'masking' to some degree that is often confused with the very dark brown to black head of the GRULLO. A foal that will shed off to BLACK or one of the variations of BROWN will be born with the silvery body colour and black points that is often mistaken for GRULLO, complete with a dorsal stripe and, oftentimes, zebra stripes on the legs and striping over the withers.

WHAT ARE THE COLOUR GENETICS OF GRULLO?

A GRULLO is the affect of the DUN gene on a BLACK base colour meaning that it shares the same colour generics as the BLACK horse and, to some degree, DUN horse. Sometimes DUN and GRULLO are confused with one another. Genetically, there are differences between them. The colour known as DUN is the affect of the DUN gene on a BAY base colour meaning a DUN and a BAY carry the agouti gene. The GRULLO does not carry the agouti gene, just as a BLACK does not. It is the inheritance of the DUN gene from at least one parent that gives both the diluted appearance as well as the DUN characteristics.

Some GRULLOS will carry the CREAM DILUTION in addition to the DUN DILUTION, which means this GRULLO may produce both DUN and CREAM DILUTION (PALOMINO and BUCKSKIN) offspring. It is commonly the result of one parent being CREAM DILUTED and the other being DUN DILUTED. However, one parent may carry both dilutions due to specific ancestors in a specific bloodline. (See DUN for the HOLLYWOOD GOLD example.) And since GRULLO has a base colour of BLACK, the CREAM DILUTION may 'hide' behind the GRULLO in exactly the same way it would the BLACK. (See BLACK) One would not be able to tell if a GRULLO carried the CREAM DILUTION by its appearance alone. These GRULLOS must be treated in the same way as one would a BUCKSKIN or a DUN carrying the CREAM DILUTION when considering the potential colour of the offspring; a DOUBLE DILUTE foal may result, if the GRULLO carrying the CREAM DILUTION is bred to another parent which carries the CREAM DILUTION, also.

HOW DID THIS HORSE GET THE DUN DILUTION?

At least one of the foal's parents contributes one copy of the DUN DILUTION gene. This parent will most likely be a DUN, RED DUN or GRULLO. There are a few exceptions. For example, some pedigrees may show a parent or ancestor as being registered BLUE ROAN but is actually GRULLO-ROAN or as being registered RED ROAN but, is actually DUN-ROAN or RED DUN-ROAN. The colours may appear to 'hide' the DUN DILUTION or appear to skip generations, oftentimes leading to the erroneous assumption that GRULLOS can be 'crop outs.' The same holds true if a parent started out as a DUN, RED DUN, or GRULW but turned gray (in the event of a gray parent), whereby the colour was amended to reflect this on the certificate of registration. In any even" DUN is a dominant gene, which means a' leas, one parent must always be a type of DUN, whether registered as a ROAN type or has turned GRAY. Bu' being dominant does not necessarily mean dominating in that, merely breeding a DUN DILUTION horse to a BLACK horse will guarantee a GRULLO or DUN DILUTE horse.

Sometimes, a GRULLO horse is the result of two DUN DILUTION parents, at least one of which would also carry the BLACK gene. This includes any combinations of crosses between DUNS, RED DUNS, GRULLOS, or horses registered a colour (erroneously or not) that is carrying the DUN gene as well-for example, a horse registered BLUE ROAN but is actually a GRULLO carrying and expressing the ROAN gene. If each parent passes on one copy of the DUN gene, the result is a horse that is homozygous for the DUN DILUTION. This means that this horse-in this case GRULLO-will pass on the DUN gene to its offspring 100 percent of the time, regardless of the colour of the other parent. And just as a BLACK horse can be homozygous for BLACK if each parent passes on one copy of the BLACK gene, the same holds true for GRULLOS. This means that the BLACK gene will be passed on 100 percent of the time  to the offspring, which means that no foals will ever have points that are red or a variation-the points will always be black to a very dark brown.

WHAT ARE SOME OTHER ASPECTS WE NEED TO KNOW ABOUT GRULLOS?

It is possible to a GRULLO to express the ROAN gene. Genetically, this is called a GRULLO-ROAN. This may happen if one parent carries the roan gene and is bred to a parent that carries the DUN DILUTION as well as the BLACK gene. Since the base colour of the GRULLO may be light in shade, the ROAN may no' be immediately recognized. At present, AQHA does no' have a separate colour choice of GRULLO-ROAN. For registration purposes, the horse is registered as the base colour of GRULLO. AQHA then indicates the ROAN characteristic under the markings area of the registration certificate with the phrase "CARRIES AND EXPRESSES ROAN GENE."

Some GRAY horses may have started out as GRULLO. These horses still retain the colour genetic information to pass on the DUN DILUTION gene and produce DUN DILUTION foals regardless of the colour of the other parent. Some GRULLOS that are turning or have turned GRAY may not easily be recognized as such, since the coat is already light in shade. A GRULLO usually shows lighter hairs in the face (sometimes called 'silvering'), specifically around the eyes and muzzle. Any true white face markings the horse was born with will blend into the face as ,he gray progresses. There may be graying in the black of lower legs. The tip of the tail will turn a pale, gold to silver colour, eventually becoming lighter from the bottom up as the horse ages. The rest of the coat may have gray hairs scattered throughout (again, this may nor be easily noticed), bu' the coat may also be unaffected for years, even retaining the DUN characteristics as it GRAYS. (See GRAY).

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