Champagne, a dominant color dilution.pdf

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Champagne, a dominant color dilution

of horses

DP Sponenberg AT Bowling

artment of Biosciences and Pathobiology, Virginia-Maryland Regional College

of Veterinary Medicine, Virginia Tech, Blacksburg, VA 2l061;

Veterinary Genetics Laboratory, School of Veterinary Medicine,

University of California at Davis, Davis, CA 95616-8744, USA

(Received 3 June 1996; accepted 2 July 1996)

Summary - Champagne dilution of horses results in a group of pale colors which have

mottled dusky skin and amber eyes. Body color varies from light brown to gold or cream.

Eye color of champagne foals is blue, and darkens to amber with age. The mating of

champagne to nonchampagne horses resulted in 54 champagne and 40 nonchampagne

foals. These results are consistent with a dominant gene (2

2.1, 1 df, P > 0.1). This

) at the Champagne (Ch) locus.

This allele dilutes black to pale brown with dark brown points, dilutes bay to yellow with

brown points, and dilutes chestnut to gold or yellow with yellow or pale points.

horse / genetics / coat color / champagne dilution

Résumé - Champagne : un gène dominant de dilution des couleurs chez le cheval. Chez

le cheval, le phénomène de dilution des couleurs appelé « Champagne» produit un ensemble

de couleurs claires allant avec une peau noirâtre tachetée et des yeux couleur d’ambre. La

couleur du corps va de brun clair à or ou crème. La couleur de 1’oeil des poulains champagne

est bleue et s’assombrit vers l’ambre avec l’âge. Des accouplements de champagne avec des

non-champagne ont donné 54 poulains champagne et 40 non-champagne, ce qui s’accorde

avec l’hypothèse d’un gène dominant 2 = 2, 1, p > 0, 10). Il est proposé que le gène

responsable de cette dilution soit considéré comme l’allèle champagne (C

INTRODUCTION

Dilution of color in horses is associated with several different genetic mechanisms,

and each mechanism results in a distinct group of colors (Sponenberg and Beaver,

1983). Early work confused some of these mechanisms, and attributed the actions

of two loci to a single locus (Castle and King, 1951; Castle and Singleton, 1961;

1 D

dilution is proposed as due to the champagne allele (C

) au locus

Champagne (Ch). Cet allèle dilue le noir en brun clair à points bruns foncés, le bai en

jaune à points bruns, et l’alezan en or ou jaune à points jaunes ou clairs.

cheval / génétique / couleur de la robe / dilution champagne

Salisbury and Britton, 1941; Singleton and Bond, 1966). The present understanding

of horse color genetics is that dilution is accomplished by three distinct genetic

mechanisms (Castle and Smith, 1953; Adalsteinsson, 1974; Van Vleck and Davitt,

1977; Adalsteinsson, 1978; Sponenberg and Beaver, 1983; Craig and Van Vleck,

1985; Lauvergne et al, 1991). This paper provides evidence of a fourth color dilution

locus for the horse.

The cremello allele at the Albino locus behaves as an incomplete dominant

(Adalsteinsson, 1974). The result of the heterozygous state is that phaeomelanin is

lightened from red to yellow, and eumelanin is unchanged. Bay is therefore diluted

to buckskin, chestnut to palomino, and black is either unchanged or diluted vary

subtly to smoky. The result of the homozygous state is that both phaeomelanin and

eumelanin are changed to cream. The skin is pink, and the eyes are blue. On any

base color the homozygous state results in cream, although subtle differences from

different base colors may persist on some horses. The cremello allele, on its own,

does not cause the distinctive striping patterns which are characteristic of another

equine dilution locus.

The dun allele at the Dun locus results in the linebacked dun group of horse

colors. It is a dominant allele, with identical appearance of heterozygous and

homozygous horses (Adalsteinsson 1974, 1978; Van Vleck and Davitt, 1977; Craig

and Van Vleck, 1985). The dun allele dilutes phaeomelanin from red to tan or light

red, and eumelanin from black to pale beige or blue. The dun allele has minimal

dilution effect on the mane, tail, and lower legs. Distinctive stripes down the back,

over the withers, and on the legs are also characteristic of the dun colors. As a result

of the dun allele, bay is changed to zebra dun, chestnut is changed to red dun, and

black is changed to grullo. The actions of dun and cremello are not additive, so that

horses with both alleles are only subtly different from those with only one or the

other. The horses with both alleles tend to retain the striping associated with dun,

and the color is diluted to the maximal extent of either the dun or the cremello

allele. Bay is changed to light gold or yellow zebra dun, chestnut to linebacked

palomino, and black to grullo. Horses that are homozygous for cremello and also

have dun are usually cream colored with striping typical of duns.

The silver dapple allele at the Silver Dapple locus is a third genetic mechanism

for dilution of horse color (Castle and Smith, 1953). The silver dapple allele is

dominant, and heterozygous and homozygous horses are similar. Phaeomelanin is

not conspicuously changed. Eumelanin is diluted to pale sepia. The dilution is

greatest in mane, tail, and lower leg. The result on black is silver dapple, the classic

form of which is a dappled sepia with very pale mane, tail and lower leg. The

action of the silver dapple allele is variable, though, and sometimes its presence is

associated with only minimal dilution of eumelanin. Bay is changed to red silver,

which retains the red body of bays but has typical changes associated with the

silver dapple allele in the mane, tail and legs. Chestnut is changed minimally, if

at all, because chestnut phenotypes are phaeomelanic, and the silver dapple allele

therefore can have no action.

A group of horse colors that is distinct from the three previous dilute color groups

consists of horses with amber eyes (which are blue a birth and then darken) and

light colors all of which tend to have a bright metallic sheen. Horses with these

colors are sometimes born a dark color, which then lightens with age. This is the

reverse of most colors of horses (Sponenberg and Beaver, 1983), and contributes to

the confusion surrounding these colors. The skin of these horses is dusky pink with

dark mottling. This skin color is darker than that of the skin of horses homozygous

for cremello and is lighter than the skin of horses with dark color or with dilute

color from the other three genetic mechanisms. The colors of this group lack the

striping typical of dun horses. This group of colors occurs in a number of breeds as

a rare variant.

One of the colors within this group of dilute colors is metallic light brown with

darker brown mane and tail, which is the color called champagne by Tennessee

Walking Horse breeders. In the past this color has been registered as buckskin

or chestnut, probably for lack of a suitable alternative designation by registration

authorities. The champagne color does not fit the definition of either buckskin or

chestnut. A second variant within the group has a yellow body and brown mane,

tail, and lower legs. This variant is frequently registered as buckskin despite the

brown (rather than black) mane, tail and legs and the eye and skin characteristics

typical of the champagne group of colors. A third variant has a gold or yellow body

and legs, and light gold or flaxen mane and tail. This color is frequently registered

as palomino although these horses have the amber eyes and mottled dusky pink skin

associated with the champagne color group, unlike the palominos arising from the

cremello allele. In addition to their occurrence in the Tennesse Walking Horse, these

colors have been noticed in Spanish Mustangs and ponies of uncertain breeding. The

group of colors including champagne was studied in order to document their mode

of inheritance.

MATERIALS AND METHODS

The complete results of mating individual champagne dilute stallions and mares

were available, and are presented in table I. These included several Tennessee

Walking Horses, and one Spanish Mustang. The matings were all to nondilute

mates. The production records of other individual horses with the champagne allele

were studied to determine the colors resulting from the presence of the champagne

allele with various background color genotypes. This included horses for which

complete records were not available, and these records are presented in tables II

and III.

RESULTS AND DISCUSSION

The matings from champagne dilute horses for which complete data were available

produced 54 champagne and 40 nonchampagne foals. Under the hypothesis that

the champagne allele is dominant, X = 2.1, 1 df, P > 0.1. This allele is proposed

as the champagne allele at the Champagne locus.

All horses that produced brown foals with brown points (the champagne color)

also produced black foals, indicating that they had genotypes capable of producing

black foals. The champagne color was never produced by horses who failed to

produce black foals. The mating of champagne horses to black mates produced

six champagne and five black foals. These findings are consistent with champagne

color being the result of the champagne allele on an otherwise black background.

Horses with gold body color and yellow or white manes and tails consistently

reproduced this color or chestnut following mating to chestnut mates. This is

consistent with the gold color resulting from the action of the champagne allele

on an otherwise chestnut background.

Horses with yellow body color and brown points only were produced by matings

that could also produce bay genotypes, and it is likely that the yellow with brown

points color results from the action of the champagne allele on an otherwise bay

background.

In some instances horses with gold bodies and light manes and tails were mated

to palomino mates. Some of the resulting foals were ivory or cream colored, with

mottled dusky skin and dark bluish green eyes. One such ivory foal was mated to

a chestnut mare and reproduced the ivory color. The ivory color is probably the

result of the heterozygous condition fo both the champagne and the cremello alleles.

If this is true, then these two dilutions are additive. Extensive breeding tests have

not yet been accomplished, but the reproduction of the ivory color from a chestnut

mare indicates that the two alleles are not at the same locus, since they appear to

be segregating independently.

Instances in which two champagne-colored horses were mated to one another

were relatively rare, and only occurred with horses for which complete production

records were unavailable. As a result, the color of homozygotes is undocumented.

In all cases of champagne-to-champagne matings, the specific color mated together

was the gold type with pale points. These matings produced 15 foals, all of which

were gold. The consistent production of the gold color suggests that the homozygous

condition of the champagne allele does not result in more extensive dilution than

does the heterozygous condition, which argues against an interpretation of the

champagne allele as an incomplete dominant. The lack of nondilute horses from

these matings is an indication that perhaps not all foals are reported. If this is the

case, then extensively diluted foals may well have not been reported.

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