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Saturday, June 4, 2016

The Cream Dilution Gene







The Cream Gene is a modifier, or a gene that acts on one of three base colours in horses.  The three base colour are chestnut, bay, and black. Some people classify brown as separate colour but for the purposes of this discussion, we will group brown with black since the inheritance is the same.

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The Cream Dilution can either be expressed as a single dilution, or a double dilution. Every chromosome has two alleles that represent the way in which each chromosome is inherited and you receive one allele from each parent. Simply put, the chromosomes (usually represented by letters) appear in pairs. To review high school biology, these pairs are generally dominant or recessive. Dominant genes are represented by two capital letters or one capital and one lower-case. The animal appears the same (phenotype) whether they are
EE or Ee. The recessive form is represented by two lower-case letters ee.


The cream gene in the single form acts upon chestnut, bay and black by diluting the red colour to cream. The Cream Colour may be light enough to appear almost white to a dark chocolate tan colour. The black is generally unaffected so bay horses horses retain the black points, and mane/tail. Black horses appear somewhat diluted- a mousey chocolate. Horses with a single Cream dilution generally have dark eyes (unless blue from paint patterns) and black skin except where there are white markings (paint markings, facial markings, and leg markings).


The double dilution, or two Cream Genes acts upon both the red and black colours. The red become light cream/off white, and the black lightens to cream. In a bay horse with two cream genes, the body colour is light cream and the points appear as a a darker shade of cream. Smokey Black Creams have a slightly over all darker shade but without genetic testing, it is impossible to determine what the base colour is in these horses. All double dilute Cream horses all have pink skin and blue or light green/hazel eyes.

BASE
ONE CREAM GENE
TWO CREAM GENES
Chestnut

Palomino

Cremello

Bay
Buckskin
Perlino (Dom Divo Perlino Yeguda)

Black
Smokey Black
Smokey Cream

Corona's Band- Six Cream Dilutes





Left to Right: Fleabitten Grey, Palomino (1), Chestnut, Palomino (2),  Palomino Paint(3), Chestnut, Corona- Dunalino ( Palomino + Dun) (4), Grey

Back Row: Chestnut,  Palomino (5), Black, Cremello (6)



Variations of Cream Dilution: Shades, Sooty, Pangaré (mealy)

Shade: A horse can be various shades of their base colour- from pale sorrel chestnut to deep liver chestnut and mahogany bay to a bay so pale it looks nearly buckskin.


Sooty- the sooty trait is another modifier that acts on coat colour. It can act alone with chestnut or bay. It gives the coat an appearance of a fine patina of black that has been airbrushed over the coat.  Chestnut horses may have the sooty modifier but it often appears isolated to the mane and tail. Some chestnut horses do have sooty on their body but it can be difficult to see. On bay horses, the sooty can be very prominent. Sooty can also be found in buckskin and palomino horses. It is possible it also can be found in darker black or brown horses but it would be difficult to differentiate due to the dark base colour.

Chestnuts


Chestnut with sooty- appears most prominently in the mane and tail, base colour is chestnut.
Cimarron
Sand Wash Basin
©Meredith Hudes-Lowder
Equus ferus -Wild Horse Photography TM








Chestnut with sooty
Cimarron
Sand Wash Basin
©Meredith Hudes-Lowder
Equus ferus -Wild Horse Photography TM













Palomino- mid colour
Bobby
Sand Wash Basin
©Meredith Hudes-Lowder
Equus ferus -Wild Horse Photography TM










Palomino- light colour (Isabella/Isabelle)
Queen Isabella de Bourbon of Spain was reputed to have a love for very pale palomino horses. She kept a stable full of pale palominos. These light palominos are sometimes called Isabella/Isabelle.Sand Wash Basin
©Meredith Hudes-Lowder
Equus ferus -Wild Horse Photography TM





Buckskin Stallion with three light palominos in his band
Buggs Band
Sand Wash Basin

©Karen McLain StudioEquus ferus -Wild Horse Photography TM


Buckskin Stallion with three light palominos in his band
Buggs Band
Sand Wash Basin
©Karen McLain StudioEquus ferus -Wild Horse Photography TM







Always get your color-oriented photos before the mud bath…
Buggs Band
Sand Wash Basin
©Karen McLain Studio





Palomino with Sooty
Bolder
Well known for changing colour as he aged, Bolder has the Sooty gene expressed almost to the maximum. Born lighter, each year he grew darker and darker.  Some liver chestnut horses that have a cream gene are called “chocolate palominos” and may be hard to distinguish from Sooty palominos but the chocolate palominos tend to be browner and the colour is more uniform and not scattered as we see here on Bolder.
Pryor Mountain
©Karen McLain Studio
Equus ferus -Wild Horse Photography TM


Palomino with sooty- Bolder and his son Echo, a light palomino
Pryor Mountain
©Karen McLain Studio
Equus ferus -Wild Horse Photography TM










Palomino with sooty restricted to the forelegs, face, and chest. Tripod, a cremello- note the pink skin around his muzzle.
Tripod & Palomino Stallion
Sand Wash Basin
©Karen McLain Studio
Equus ferus -Wild Horse Photography TM







BAYS


Sooty Bay
McCullough Peaks
©Meredith Hudes-Lowder
Equus ferus -Wild Horse Photography TM











YELLOW ARROWS= Bay with Sooty
PINK ARROW= Bay
GREEN ARROW= Primitive Bay or Bay with Pangaré
A Primitive Bay is a bay with paler colour and the black points of the legs do not extend above the knees/hocks- often paler in comparison.
McCullough Peaks
©Karen McLain Studio
Equus ferus -Wild Horse Photography TM




YELLOW ARROWS= Bay with Sooty
PINK ARROWS= Bay
McCullough Peaks
©Karen McLain StudioEquus ferus -Wild Horse Photography TM










Buckskin Stallion
Sand Wash Basin
Buggs
©Karen McLain Studio
Equus ferus -Wild Horse Photography TM










Buckskin Mare with her Cremello colt
McCullough Peaks
©Meredith Hudes-Lowder
Equus ferus -Wild Horse Photography TM










Buckskin Mare- slight Sooty
McCullough Peaks
©Meredith Hudes-Lowder
Equus ferus -Wild Horse Photography TM







Buckskin Mare- moderate/heavy Sooty
McCullough Peaks
©Meredith Hudes-Lowder
Equus ferus -Wild Horse Photography TM






Like the Sooty modifier, the Pangaré (mealy),
trait may appear with most coat colours and lighten the coat on the legs, belly, and around the muzzle. Common in Icelandic and Haflinger horses.













Genotype at the agouti locus
Chestnut horses
Palomino horses
A+_
Light chestnut
Cream palomino
AA_
Red chestnut, with AAAA being the reddest
Golden palomino
At_
Standard chestnut
Seasonal palomino
Aa Aa
Liver chestnut
Chocolate palomino


Bibliography
Gower, J. (1999). Horse color explained: A breeder's perspective. North Pomfret, VT: Trafalgar Square.

Kathman, L. (2014). The equine tapestry: An introduction to horse colors and patterns. Charlotte, NC.: Blackberry Lane Press.

Sponenberg, D. P. (1996). Equine color genetics. Ames: Iowa State University Press.

Presented by Dr Meredith Hudes-Lowder

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Hudson Valley, New York, United States