Some very basic information about equine coat colour genetics. Please email or phone if you have any questions. Kate and Leanne both keep up with the latest developments in the world of equine colour genetics and are able to explain it in terms that are easy to understand.
THE CREAM GENE
To start with, there are only two base coat colours in all horses – black and red (chestnut). All other colours and patterns you see are caused by modifying genes expressing (working) on the base coat colour. All genes come in pairs, so a horse has two genes for base coat – horses that look black have either black and black (shown as EE on a DNA test) or black and red (Ee) and horses that look chestnut have two red base coat genes (ee on a DNA test). Red is recessive, which means it can ‘hide behind’ black, so many black horses carry a chestnut gene but you can’t ‘see’ it. A chestnut horse has only two red base coat genes, there is no gene for black in a chestnut horse.
These two colours, black and chestnut, can get modified into all the other colours we see. For instance, if you have a black horse, and add one or two genes for, say, bay (Agouti, shown as A on a DNA test; ‘homozygous for Agouti’ is shown as AA, one copy of Agouti is Aa and no agouti at all is aa) then the black horse will now look bay. If you then add, say, one copy of Cream (shown as Cr on the DNA test – so it will read Cr cr ) it will dilute the bay to buckskin. If you add another copy of Cream (so the DNA test will read Cr Cr ) it will dilute the hair further and also dilute the skin to pink and the eye colour to blue. Agouti only expresses on black, so you only ‘see’ it on horses with a black base coat – a chestnut horse can carry one or two copies of Agouti and you won’t even know it’s there because it doesn’t express on red.
The Cream gene is responsible for creating Palominos and Cremellos on red base coated horses, and it creates Buckskins and Perlinos on black base coated horses. If you have a chestnut horse, and add one copy of Cream (so one parent must have carried Cream, and passed it on to the foal), it will dilute the chestnut coat to gold, and the mane and tail to cream/white. If you have a second Cream gene, it will dilute the coat further to a pale gold, and the mane and tail will be white.
One copy of cream will dilute the red coat of a bay horse to gold, but Cream can’t express on black – meaning it ‘won’t work on black’. So, the black mane, tail and legs of a bay horse remain black when you add the Cream gene to create a Buckskin horse. This means, if you have a black horse (so he doesn’t carry agouti – he is EE aa on a DNA test) and add one copy of Cream, he will still look black as one copy of Cream cannot dilute black – these can be called ‘black buckskins’ or ‘smoky blacks’ and though they look black to the untrained eye, the Cream gene is there and these horses can still have Palomino or Buckskin foals, and, if mated to a horse that also carries Cream, they can have double cream dilutes. Brown horses (a black horse with brown agouti) have more black in their coats than bays, so Cream on a brown horse creates the range of burned or brown buckskins, which can be dark gold or sometimes almost look the same as brown. If there is a lot of black in the coat, the cream gene can’t dilute that, so you can get very dark buckskins. If you add a second copy of Cream to a black/bay/brown it will now dilute the black and you get a Perlino – a pale gold horse with a slightly darker mane and tail and legs (sometimes the mane and tail and legs look almost the same colour as the coat, sometimes they can be a dark caramel colour).
Double Cream Dilutes (Cremellos and Perlinos) have two Cream genes so all their offspring will get a Cream gene from them, so all their offspring will be dilutes. If you mate a Cremello (two Cream genes, two red base coat genes) to a Chestnut, you can only ever get Palomino. If you mate the Cremello to a black, bay or brown, you can get Buckskin, or you can get Black Buckskin/Smoky Black if neither parent passed on Agouti, or you can get Palomino if the black/bay/brown horse had a chestnut gene (remember, chestnut is recessive so it can hide behind black – a horse can look black and still have one chestnut gene). If you mate the Cremello to a Palomino you will get either Cremello or Palomino (a 50/50 chance). If you mate the Cremello to a Cremello, you will only ever get Cremello.
A Perlino may have two Black base coat genes (Ee), or one black and one red (Ee), so Perlinos with EE will only ever throw buckskins to non-dilute mares (they can only drop a Black base coat and a Cream gene). A Perino with one Black and one Red basecoat can throw either Palominos or Buckskins to non dilute mares.
Any horse with a Cream gene must have at least one parent carrying a Cream gene – it doesn’t just ‘appear’. Any Cremello or Perlino must have both parents carrying dilute genes. Once a Cream dilute horse has a foal that isn’t carrying Cream (so it is a Chestnut, Bay, Black, Brown) then the that horse is no different from any other Chestnut, Bay, Black or Brown – you don’t get horses that are ‘nearly Palomino because their sire was a Palomino’: either the Cream gene is there and the horse is a dilute, or it isn’t there.
THE SILVER GENE
Silver, called Taffy here in Australia for over 100 years, works differently from Cream, though it still dilutes the coat colour. Where Cream only expresses on red (so horses need to have red in their coats, they can’t be plain black), Silver only expresses on black. A Chestnut horse carrying one or two copies of Silver (‘Z’ on a DNA test) looks like any other chestnut, but if you add Silver to a Black horse with no Agouti, the black coat is diluted to a dark chocolate and the mane and tail are diluted to a range of colours from ‘mud with cream highlights’ to almost pure white. If the horse has bay Agouti, the Silver gene can’t dilute the red of the bay coat colour, but it can still dilute the black of the mane, tail and legs and you can get a very pretty coloured horse that may look like a flaxen maned liver chestnut.
Horses carrying Silver look the same whether they have one or two copies of Silver, unlike the Cream gene horses who are Palominos and Buckskins with one copy of Cream and Cremellos and Perlinos with two copies of Cream.
If you want to breed for Silver, it is best to use breed Silver to Silver or Black to Silver. If a horse is homozygous Silver (so it’s DNA test is ZZ), then it will only have foals carrying Silver.
THE DUN GENE
Dun is also a dilution gene. It is often confused with Buckskin, but it is a separate dilution gene, though many Buckskins may also carry Dun. Many horses carry false dun factors but true Dun dilutes the base coat and leaves a darker, ‘painted on’ dorsal stripe that runs all the way from the wither down into the tail. Duns may also have any or all of these factors: striping on the legs, shadowing on the shoulder, lighter guard hairs in the mane or tail, ear tipping, cobwebbing or masking on the face. The most important factor is the dorsal stripe, though some horses with what appears to be a dorsal stripe test negative for the gene on a DNA test, so it can be a ‘false dun factor’.
Homozygous Duns will only ever have Dun foals. A horse that is Black without Agouti and which has Dun is called ‘Grulla’. Sometimes people call brown or black buckskins or even dark grey horses ‘Grullas’, but the true Grulla is a black horse, no Agouti (so not bay or brown) with Dun.
CHAMPAGNE
See the page on Champagne.
Champagne is a dilution gene closely related to Cream in that it creates colours similar to Palomino and Buckskin, but it can dilute black, it partially dilutes the skin colour and eye colour and it is no different in single or double form (whereas Cream only dilutes the coat colour in single form and fully dilutes the skin and eye colour in double form).
PEARL
Pearl is a dilution gene that is an ‘incomplete recessive cream activated dilution gene”. A horse carrying one copy of Pearl looks almost the same as any solid coated horse, perhaps just a tiny bit lighter in both coat and skin colour. If the horse carries Cream as well as Peark, the Pearl gene is ‘activated’ and the horse looks similar to a Perlino. If the horse has two copies of Pearl, it gives an ‘apricot colour’ on horses with a chestnut base coat and the bay/black/brown colours also go lighter – it isn’t as light as a double cream dilute (Cremello, Perlino), looking more like a light coloured Champagne. There are only a handful of Pearl horses in Australia.
GREY
Grey is a colour mutation that overrides all other colour genes. If a horse has the grey gene, the full life of the coat colour ‘floods’ the hairs in the space of a few years, which is why greys are often darker than other horses in the first few years, and then the hairs have no colour left and are grey. Even if a horse is born Cremello, Palomino, Buckskin, Dun, Pinto or any other colour and goes grey, it is called grey – the base coat colour is gone.
And always remember the Murphy's Law of Colour Breeding: if you have a 50% chance of getting the colour you want, there's a 90% chance that it will be the colour you don't want! |
