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Horse Coat Colours and Markings

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Horse Coat Colours and Markings HorseHorse CoatCoat ColoursColours andand MarkingsMarkings Cindy Harper Onderstepoort Laboratory for Applied Veterinary Genetics BasicBasic ColoursColours Black Bay Chestnut GeneticGenetic ControlControl ofof thethe BasicBasic ColoursColours MelanocytesMelanocytes produceproduce melaninmelanin pigmentpigment 22 PigmentsPigments responsibleresponsible forfor coatcoat andand skinskin colourcolour –– eumelanineumelanin (black(black andand brown)brown) andand phaeomelaninphaeomelanin (red(red andand yellow)yellow) ColourColour genesgenes controlcontrol eithereither thethe pigmentpigment producingproducing cellcell oror pigmentpigment productionproduction 22 genesgenes controlcontrol thethe mainmain colourcolour switchesswitches inin horseshorses ExtensionExtension (E)(E) andand AgoutiAgouti (A)(A) GeneticsGenetics Locus (address of a gene and each has a name) occurs on a pair of chromosomes – 1 from sire and 1 from dam Sire Dam Form of gene (allele) on 1 chromosome of pair can be same as on other – homozygosity Or different – heterozygosity Different – dominant and recessive where 1 allele is expressed and other is not Function: Gene that codes for protein Protein: Effect e.g. stimulates melanocyte to produce eumelanin Chromosome pair Result: Black horse TheThe ExtensionExtension Gene/LocusGene/Locus (E)(E) Difference between black and red lies in the action of 1 gene – MC1R Allele symbols are E and e E extends black (eumelanin) in coat e extends red (phaeomelanin) in coat Combination of alleles at the extension locus: EE Allows black in the coat: Black, brown, bay, Ee buckskin, grullo Black in the skin but not in the coat: Chestnut, ee palomino BlackBlack PatternPattern TheThe AgoutiAgouti GeneGene // LocusLocus (A)(A) AA Black pattern limited to the legs , mane and tail Aa aa Black distributed uniformly through the coat The combination of alleles at the extension and agouti genes / loci control the basic colour of the horse InteractionInteraction betweenbetween ExtensionExtension andand AgoutiAgouti EEAA EEAa Black in coat Bay, Brown EeAA Black at the points EeAa EEaa Black in coat Eeaa Black throughout coat Black, eeAa eeAA Only red in the coat coat Chestnut, eeaa RedRed FactorFactor (e)(e) ExtensionExtension locuslocus –– 22 allelesalleles EE andand ee eeee breedingbreeding principlesprinciples Chestnut + chestnut = all chestnut ee e ee ee e ee ee RedRed FactorFactor ((EeEe)) andand BlackBlack PatternPattern factorfactor ((AaAa)) chestnut + chestnut = All chestnut Sire: eeAa Extension (red) locus chestnut dominant over the Agouti (black) locus eA ea ea eeAa eeaa Dam: eeaa chestnut ea eeAa eeaa RedRed FactorFactor ((EeEe)) andand BlackBlack PatternPattern factorfactor ((AaAa)) Sire: EEaa black Ea Ea eA EeAa EeAa Bay Bay eA EeAa EeAa Dam: eeAA chestnut Bay Bay RedRed FactorFactor ((EeEe)) andand BlackBlack PatternPattern factorfactor ((AaAa)) Sire: Eeaa black Ea ea Ea EEaa Eeaa Black Black ea Eeaa eeaa Dam: Eeaa black Black Chestnut BreedingBreeding BlackBlack AvoidAvoid recessiverecessive e!e! GeneticGenetic testtest forfor E/eE/e IsIs thisthis aa truetrue blackblack ((aaaa)) oror darkdark baybay // brownbrown ((AaAa)?)? GeneticGenetic testtest forfor A/aA/a PrinciplePrinciple Each horse has all the genes that can possibly code for any colour, BUT an individual allele combination that in total gives it a specific appearance! Extension Locus Agouti Locus Cream Locus Grey Locus Tobiano Locus E e A A CR N g g TO N 1 2 3 4 5 Genotype: E/e A/A N/CR g/g N/TO Phenotype: Diluted Bay (Buckskin) Non- grey with a Tobiano Paint pattern WhatWhat colourcolour?? BasicBasic ColourColour ModificationModification SootySooty // ShadedShaded BlackBlack hairshairs betweenbetween coatcoat hairshairs BayBay –– toplinetopline toto extensiveextensive coveringcovering mostmost ofof thethe bodybody BasicBasic ColourColour ModificationModification SootySooty // ShadedShaded BayBay –– extensiveextensive shadingshading ““BrownBrown”” HowHow toto distinguishdistinguish fromfrom truetrue black?black? GeneticGenetic testtest aaaa –– blackblack // AaAa oror AAAA -- brownbrown TheThe BrownBrown GeneGene ThereThere isis aa brownbrown genegene –– (TYRP1)(TYRP1) dilutesdilutes blackblack toto chocolatechocolate MostMost obviousobvious inin dogs,dogs, butbut notnot commoncommon colourcolour inin horseshorses andand chocolatechocolate andand dundun horseshorses areare causedcaused byby otherother genesgenes WhenWhen isis aa horsehorse Brown?!Brown?! BrownBrown inin horseshorses isis aa termterm usedused toto describedescribe aa shadeshade ofof baybay inin horses.horses. SomeSome breedersbreeders describedescribe allall baysbays withwith shadingshading // sootinesssootiness asas BrownBrown SomeSome breedersbreeders describedescribe allall baysbays regardlessregardless ofof shadingshading asas baysbays MostMost commonlycommonly breedersbreeders describedescribe thethe dark,dark, extensivelyextensively shadedshaded baybay asas brownbrown andand allall otherother baysbays asas baybay Heritability?Heritability? BrownBrown HeritabilityHeritability Some believe that brown can be bred and is in fact a sub-division of the agouti locus or extension locus (At or EB) Black is allowed in the coat and is more extensive than the points in a bay This would support the proposal that brown (“extensive bay”) is heritable and “breedable” ColourColour termsterms TermsTerms thatthat describedescribe aa phenotypephenotype –– whatwhat youyou seesee DependDepend onon breedbreed // societysociety // countrycountry // individualindividual OnlyOnly rightright oror wrongwrong isis toto findfind andand testtest thethe actualactual geneticgenetic control!control! FEIFEI rulebookrulebook statesstates thatthat thethe definitiondefinition ofof colourcolour differsdiffers accordingaccording toto country.country. BasicBasic ColourColour ModificationModification SootySooty // ShadedShaded ChestnutChestnut –– usuallyusually distributeddistributed throughoutthroughout thethe coatcoat LiverLiver ChestnutChestnut BasicBasic ColourColour ModificationModification MealyMealy MealyMealy causescauses lighterlighter areasareas onon thethe belly,belly, muzzle,muzzle, innerinner legs,legs, andand overover thethe eyes.eyes. ItIt isis usuallyusually ignoredignored inin colorcolor description.description. BlackBlack -- SealSeal brownbrown (test(test aaaa isis modifiedmodified blackblack // AaAa oror AAAA isis baybay withwith lotslots ofof shading)shading) ChestnutChestnut toto sorrelsorrel forfor breedersbreeders ofof draftdraft horseshorses MealyMealy Dun Bay BayBay BlackBlack PointsPoints LegsLegs EarEar tipstips ManeMane TailTail VariationsVariations ofof BayBay BlackBlack • No Brown in coat • White markings are allowed •Genetic test aa vs Aa or AA and EE or Ee FeatureFeature ofof BayBay vsvs BlackBlack AA blackblack horse,horse, eveneven withwith aa sunsun--bleachedbleached hairhair coatcoat willwill havehave solidsolid blackblack hairshairs aroundaround thethe eye.eye. Bay Black ChestnutChestnut ee e ee ee e ee ee Recessive traits are expressed phenotypically when in homozygous form! Red coat throughout – no black points. ChestnutChestnut ModificationsModifications Liver Flaxen Flaxen and mealy WhiteWhite onon basicbasic coatcoat AnyAny whitewhite oror whitewhite patternpattern isis SUPERIMPOSEDSUPERIMPOSED onon aa basicbasic colourcolour CoverCover thethe wholewhole oror partpart ofof thethe horsehorse PatternPattern –– namename GreyGrey RoanRoan RoaningRoaning SpottingSpotting PaintsPaints WhiteWhite markingsmarkings GreyGrey BornBorn anyany colourcolour –– becomesbecomes greygrey UsuallyUsually startsstarts onon headhead andand isis progressiveprogressive SpeedSpeed ofof greyinggreying individualindividual GradualGradual processprocess –– completelycompletely whitewhite withwith pigmentedpigmented skinskin GreyGrey BreedingBreeding DominantDominant traittrait GGGG andand GgGg –– alwaysalways greygrey i.e.i.e. aa horsehorse doesdoes notnot carrycarry aa hiddenhidden greygrey genegene AA greygrey foalfoal mustmust havehave atat leastleast 11 greygrey parent!parent! GG HomozygousHomozygous greygrey ++ nonnon Gg greygrey 100%100% GreyGrey g Gg g Gg Gg GreyGrey BreedingBreeding A horse can have any combination of base coat genes, but G overrides all e/e a/a N/RN to/to C/C G/g = GREY Grey is going to obliterate any other colour pattern 2 greys can produce a non-grey Gg DNA Test available G GG Gg g Gg gg GreyGrey VariationsVariations VariationsVariations ofof greygrey cancan givengiven differentdifferent names:names: Rose grey Fleabitten grey Steel grey Dapple grey RoanRoan PermanentPermanent colourcolour,, whitewhite doesdoes notnot progressprogress withwith age!age! DarkDark headhead andand limbslimbs CharacteristicCharacteristic invertedinverted ““VV”” aboveabove kneesknees RoanRoan GeneticsGenetics RNRN isis causedcaused byby aa dominantdominant gene.gene. RNrnRNrn oror rnrnrnrn (not(not roan)roan) –– nono testtest yetyet THUS:THUS: AA roanroan mustmust havehave 11 roanroan parent!parent! HomozygousHomozygous dominantdominant roanroan RNRNRNRN == lethallethal resorptionresorption?? RoanRoan VariationsVariations Chestnut Roan Blue Roan RabicanoRabicano // RoaningRoaning Rabicano, also called white ticking or roaning, is characterized by limited roaning in a specific pattern, usually in the flank, sides and the tailhead Also in breeds which do not possess any true roan Thoroughbreds and Arabians SpotsSpots THETHE LEOPARDLEOPARD COMPLEXCOMPLEX ProducedProduced
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