Enloe Quarter Horses Specializing in Grulla Quarter Horses and Grullo Quarter Horses and Dun Factored Performance Horses

Base Colors and Modifiers
Base color on a horse is the true color that exists under other modifying genes. Base colors may be "hidden" or "masked" under gene modifiers like the gray gene and the roan gene. Typically, a foal is born a "base color" and gene modifiers change the appearance of the coat over time. For example, a horse may be born grullo base colored, and over time, turn gray or blue roan if the horse inherits the modifier from one of its parents. Genes work in a hierarchical path as displayed below. That is, a horse's color pattern could be thought of as "layers" over "layers". If the gene exists in dominant form, the horse will exhibit the following color, regardless of the genes below it.

Rank in Dominance	Gene	Dominant Value Displayed A gene is made up of two alleles, one inherited from each parent	Definition
1	Gray	GG or Gg	The horse will have a gray appearance
2	Roan	RnRn or rnrn	This horse will have a roan appearance
3	Dun	DD or Dd	This horse will have a dun appearance with a diluted body and dun factor characteristisc
4	Cream	CcrCcr or CcrC	This horse's body coat will be diluted
5	Agouti	AA or Aa	This is an attachment gene and only visible if a dominant E exists. If a horse has a dominant E, it will have black points. The Agouti in dominant form prints the color pattern as a brown body with black points (like a bay, dun, buckskin) as opposed to the homozygous recessive form (aa) where the coat pattern is a full black body as seen in grullo, black and blue roan. Horses without black points like sorrel, palomino, chestnut and cremello may carry a gene pattern of AA, Aa, or aa, but it is not displayed and all body patterns remain brown. This is why you never see a black bodied horse with brown legs and why some non-black pointed horses (coded as aa) produce lots of black and grullo horses, some (coded as Aa) occasionally produce black and grullo, and some (AA) never produce black or grullo. Remember, a grullo is aa, and if the parent is AA, it has no recessive "a" to throw to its foal.
6	Red Factor	EE or Ee	Controls black points on a horse. If a horse has at least one dominant E, the horse will have black points

So, from the table above, because the gray gene masks other genes, we can deduce that a gray horse can have any base color from sorrel to buckskin to grullo. In fact, a gray horse can also carry all the gene modifiers and patterns listed above.

Quick review of some other color patterns
Grouped as (Red Factor E, Agouti A, Cream C, Dun D, Roan Rn, Gray G)

Why do some gray horses produce lots of buckskins or grullos?
This has to do with the horse's base color, and a little luck. If a gray horse has a base color of buckskin (E?,A?,Ccr?, dd, rnrn, G?), it will be more likely to reproduce the buckskin base color than a gray horse with a base color of sorrel trying to produce a base color of buckskin. The same holds true for a grullo base.

Interestingly, a gray horse with a pattern of (E?, AA, ??, ??, ??, G?) will NEVER produce a grullo because of the Agouti AA. It has no recessive "a" to pass to its offspring. On top of the base color, a breeder must assume 50% of the horse's foals will turn gray, making gray a poor way to produce grullo. Although gray appears to be a color close in nature to grullo, it is actually considered a poor grullo producing color in relation to other colors. Roan affects colors similarly to the gray gene and those wanting to produce a pure grullo color should steer away from roan carriers, including blue and grullo roans.

Comments about this article may be sent to: Kristy Enloe at Visit Enloe Quarter Horses/Horse Color Genetics Message Board to post color questions!

Comments about this article may be sent to:
Kristy Enloe at Visit Enloe Quarter Horses/Horse Color Genetics Message Board to post color questions!