Shetland Pony Coat Colour Genetics
BASE COAT COLOURS
There are three base coat colours, black, chestnut & brown/bay. These colours stem from a pigment, formed by the melanocytes, called melanin. The melanocytes can make two different kinds of pigment. The black pigment eumelanin (which gives rise to black ponies) and the red pigment phaeomelanin (which gives rise to chestnut ponies). The brown or bay ponies occurs when the hairs are coloured alternately with both eumelanin and phaeomelanin. Whether the ponies melanocytes form eumelanin, pheaomelanin or a mixture of the two, is decided by the ponies genes. Besides the three base coat colours there is a large number of other colours, which are all modifications of the three base coat colours, they have all arisen from mutations in the ponies colour coding genes.
( The dominant genes are designated with an upper case letter and the recessive genes are designated with a lower case letter)
The three base coat colours are controlled by two genes or so called loci. A locus is a specific location on the chromosome. Genes that have the same locus are called alleles. Each locus has at least two alleles. the two series of alleles controlling the base coat colours are :- The A Series Which consists of four alleles, that determine the base coat colours pigment pattern. Meaning the distributation of eumelanin or phaeomelanin on the ponies body. Agouti means striped, and here the hair changes colours from root to tip. phaomelanin is present at the root and eumelanin is present at the tip of the hair. A + Agouti Wildtype :- Eumelanin is restricted to the pasterns and possibly the front knees and the hocks. The mane and tail are also eumelanic (meaning black). A Agouti :- As above , but here the eumalanin is distributed further up the legs at tan points or eumelanic and tan. Results in eumelanin on most of the body, or a mixture of eumelanin or phaeomelanic hairs, with strictly phacomelanoc hairs on smaller areas (for instance behind the ears, on the flanks and on the insides of the thighs). Mane and tail are eumelanic (Black). a Non Agouti :- Results in an evenly coloured pony with eumelanin across the entire body. The E Series Which consists of three alleles that determine the distributation of eumelanin. ED :- Results in a dominant distribution of eumelanin meaning plain eumelanic. E :- Results in normal distributation of eumelanin, allowing cumalin on the areas determined by the allels of the A locus. e :- Restricts eumalnin, giving rise to at distributation of phacomlanin to the entire body. The effect of the A locus is hereby annuled.
The pony always receives/inherits two alleles in each locus, one from the stallion and one from the mare. When a gene is dominant, it only needs one allele of the gene, for the colour to show through. If the gene is recessive, it needs to ocupy both alleles in the locus for the colour to show through. When a colour shows through (meaning you can see the colour on the pony) it is because of the ponies phenotype. The colours the pony is carrying, but which does not show through, is part of the ponies genotype. When a pony has two alleles of the same gene (for instance ee) it is said that the pony is homozygous for that particular gene. If the pony has two fifferent alleles of a gene (for instance Ee) then the pony is heterozygous for that gene.
There are both recessive and dominant black ponies. The genotype aa B_E_ results in a plain black Pony (recessive black). The genotype ED_B_ results in a plain black pony (dominant black). Since the ED allele is epistatic to the alleles in the A series and dominant to the rest of the of the alleles in the E series, these alleles will have no influence on the colour in the presence of the ED allele. Black ponies are not always equally black. Very black ponies might have the Sty factor or maybe genotypically recessive black and dominant black at the same time. Pigment density can help explain why some seem to be more black than others.
Probably the most difficult to genotype, there are so many different shade of chestnut that it is almost impossible to keep track. Some examples :-
The genotype ee will always result in a chestnut pony no matter the genes in the A and B series, and the genotype bb will always result in a chestnut pony, no matter the genes in the A and E series.
The genotype A_bb E_ results in a chestnut pony with brown legs, mane and tail.
The genotype ee A+_ results in a very light chestnut, like the colour seen in the Haflinger .
Both the genotype ee AA and the genotype ee At_ results in a chestnut pony (Red chestnut, where the coat shines red and standard chestnut where the coat shines yellow).
The genotype ee aa results in a dark red chestnut pony ( liver chestnut)
Mulberry (in english) or (sorrel in american) is the designation for a chestnut pony with a flaxen mane and tail.
Pigment density and the sty factor can also influence the red nuance in the chestnut pony
BROWN / BAY PONIES
The brown or bay colour is a modification of the black base coat colours. This is why sometimes brown or bay is not counted as one of the base coat colours. It has a dominant inherritance pattern, meaning that only one allele of the gene is necessary for the colour to show through. The colour will need the pony to carry at least one allele for black to be able to show through.
The genotype A_B-E_ (it can be either dominant or the recessive allele) results in a light brown pony with black legs, mane and tail. If the pony has A+ instead of A the black on the legs is restricted to the pasterns and possibly the front knee and the hocks. If the pony also has the Sty gene it will be a darker , almost chestnut brown pony, that diffuses to almost black in the head and on the back, this is what is called bay (red bay, blood bay, mahogany bay or dark bay )
The genotype at_B__E_ results in a dark brown pony with tan points behind the ears, on the flanks and inner thighs, mostly spots whwere the ponys skin is thin. The hair consists of a mixture of black and red hairs, and the colour is darkest along the back. The long hairs, the mane and tail are still completely black. This colour is called brown, if the pony also has a Sty factor it would result in a black brown pony that is practically completely black, but with a hint of red brown areas in the thin skinned spots, this is called black brown.
A SUMMARY OF THE BASE COAT COLOURS
Chestnut ponies never carry the gene for black, but they can be carriers of the gene for brown/bay. Black ponies never carry the gene for brown/bay, but they can be carriers of the gene for chestnut. Brown/bay ponies always carry one or two alleles of the gene for black, and can be carriers of the gene for chestnut. This means that two chestnut ponies will never be able to have any foals with chestnut base coat colour. Two black ponies will be able to have both black and chestnut foals. Two brown/bay ponies will be able to have both chestnut, black and brown/bay foals…………..When testing for base coat colours usually only the A locus and the E locus are looked at, which means that the type or nuance of the colour is not known. For instance it doesn’n distinguish between brown or bay ponies
EE aa = Black
Ee aa = Black ( carrier of chestnut )
ee aa = Chestnut
ee Aa = Chestnut (carrier of Brown or Bay)
ee AA = Chestnut 9homozygous carrier of Brown or Bay)
EE Aa = Heterozygous Brown or Bay
Ee Aa = Heterozygous Brown or Bay (carrier of Chestnut)
EE AA = Homozygous Brown or Bay
Ee AA = Homozygous Brown or Bay (carrier of Red)
Results in an expression of eumelanic pigment. in the brown or bay pony, the allele has the strongest effect along the back of the pony. In the chestnut pony the allele has a more uniform effect on the whole body. (for black see above). The gene is dominant, which means that only one copy of the Sty allele is needed to get the effect. Also it is enough that either the mare or the stallion has the gene for the foal to inherit it.
FLAXEN MANE AND TAIL
Flaxen = A light mane & tail on a chestnut pony results from the f- series, which consists of two alleles. F Creates a normal colour, meaning chestnut mane and tail in the chestnut pony. f results in a light/straw, cream or white mane and tail in the chestnut pony. The effect of the gene is only seen in chestnut ponies, but the gene can be carried hidden in ponies of other colours. Since the gene is recessive, two alleles are needed to create an effect……… ……………… FF = no effect…… Ff = no effect..( but heterozygous carrier of the allele )………ff = effect (and homozygous carrier of the allele)………. Both the mare and the stallion need to carry the allele, for the foal to recieve a flaxen mane and tail. If both the mare and stallion has the colour, then they will both be homozygous for the allele and will therefore both pass on the allele to the foal, resulting in a foal with flaxen mane and tail.
GREY AND ROAN PONIES
There are two types of pony in which their colour is diluted by the mixture of white hairs :- The fading and the permanent. Both genes result in white hairs being mixed with the ponies normal colour, The grey pony will have progressively more and more white hairs mixed in the older they get until they are completely white. The roan ponies do not and will never be completely white. A few roan ponies will get a few more white hairs mixed in with age, but not at all to the same extent as grey ponies. The Roan Pony can show very great variations in their colour depending on the seasons, which is why they are also called colour alternators Ponys that carry both G and R (see below) look like roans as foals but this will soon fade.
The Grey Pony results from the dominant allele of the G series Which contains two alleles. G gives a continous and progressive mixture of white hairs in with the normal colour, until the pony is completely white. g has no effect on the normal colour. The foal fur can be any colour and only as the pony grows, the white hairs start to appear. Depigmentation of the skin can occur in grey horses as they get older, especially around the eyes and muzzle, which results in flesh coloured skin. The gene is dominant and is expressed in ponies both heterozygous and homozygous for the dominant allele. This means that as long as either the mare or the stallion is grey, then the foal has a possibility of turning grey as well
Roan ponies always have more than 50% white hairs in the coat. Ponies with less white hairs are not considered to be roan. The roan colour appears when the foal fur is shed. A black pony with the roan gene is called blue roan. A bay is called a red roan (despite being bay and not chestnut). A chestnut is called a strawberry roan. R results in a roan pony. r no effect, normal colour. The gene is dominant, resulting in the colour being transmitted in both heteroztgous and homozygous ponies. As long as the mare or stallion is roan there is the possibility of a roan foal.
There are a number of genes that either dilute the ponies base coat colour or modify the pigment so that the colour looks lighter.
The dun coloured ponies all carry alleles from the D series. A black pony with one or two dun alleles become blue dun ( grullo ), a brown or bay pony becomes golden dun ( zebra dun ), and a chestnut pony becomes a cream dun ( red dun ). D dilutes both eumelanin and phaeomelanin. The body and neck are diluted more than the legs and the head which are darker. Down through the middle of the mane, back and tail is a long dark stripe ( known as the dorsal or eel stripe ) d = normal pigmentering. The gene is dominant therefore only the mare or the stallion has to be dun for a foal to have the chance of inhereting the colour.
The dorsal stripe and slight leg barrings might be visible on ponies of other colours. These are pseudo-dorsal stripes. Ponies with pseudo-dorsal stripes are not dun and will not be able to breed dun coloured foals. A pseudo-dorsal stripe is often not as distinct as the dun dorsal stripe, and often will not be visible all year round.
From the C series comes the colours palomino, buckskin and smoky black. The C series is also called the albino series, because in some animal species there is a third and completely recessive allel c = the albino allele which is responsible for the true albinos that lack pigment in both skin, hair and eyes, giving them the caracterristic red eyes seen for instance in rodents. This allele however does not exist in ponies, which is why there are no true albino ponies. C has no effect on the base coat colour and results in normal colour… Ccr Dilutes phaeomelanin but not eumelanin, and it exerts a stronger effect on the long hairs (mane & tail) than the hairs of the body the allele therefore dilutes chestnut & brown or bay ponies, but not black ponies. The chestnut horse with 1 allele of the cream gene ee CcrC will be palomino. However just as there are differentshades of red in the chestnut ponies, there are also different shades of palomino ponies. The genotype ee A+_CcrC results in a very light yellow colour. The genotype ee AA CcrC results in a more golden palomino that does not lighten in the winter (non- seasonal palomino). The genotype ee At_CcrC results in a palomino that lightens in the winter (seasonal palomino). The genotype ee aa CcrC results in a very dark palomino with an almost brown coat colour which can be mistaken for a mushroom or silver pony. The seasonal palominos are born very light, and the golden colour does not appear until they shed the foal fur. Non seasonal or true coloured palominos are born a little darker, and they keep the colour all year round……….. Brown or bay ponies that recieve one allele of the cream gene will be buckskin that is yellow to brown with a black mane and tail. Buckskin should not be confussed with golden dun, because bucskin ponies do not have a dorsal stripe. Buckskin ponies come in a variety of different shades depending on the genotype of the base coat colour. The genotype E_A+_CcrC results in a very light buckskin (cream buckskin)…. The genotype E_AA CcrC results in a warm yellow colour (golden buckskin). …The genotype E_At_CcrC results in a normal buckskin (standard buckskin). Black ponies that recieve one allele of the cream gene is called golden black or smokey black. Most often you will not be able to see that a black pony is carrying the cream gene, although sometimes it has a golden sheen to its coat especially in the summer time. When a pony recieves two alleles of the cream gene it is called a pseudo albino or blue eyed cream. These ponies are very light, almost completely white and have light blue eyes, white hooves and pink skin. They are not true albinos. The blue eyed cream ponies look almost exactly the same whether their base coat colours are chestnut, brown or black, but there are still different names for the three genotypes…. A chestnut pony with two alleles of the cream gene is called cremello….. A brown or bay pony with two alleles of the cream gene is called perlino …. ….. …….. A black pony with two alleles of the cream gene is called smokey cream. Because the cream gene is dominant, only one allele is needed for a dilution of the base coat colour to occur. This also means that a blue eyed cream pony which always passes on a cream allele will aways make a palomino, buckskin or smokey black foal. For instance a cremello pony will always result in a palomino foal when bred to a chestnut pony.
It appears that all mushroom shetland ponies are the result of a completely new and undiscovered gene, and since the gene has yet to be mapped nothing can be said with certainty. It is controlled by the S series which has two alleles S and s … S dilutes eumelanin but has no effect on phaeomelanin. Mane and tail are diluted more than the hairs of the body…. s = normal colour, no dilution. Black and black/brown ponies are diluted to a dark grey, blue grey or dark chocolate colour, with light grey or white mane a nd tail. Bay ponies are only diluted slightly on the body, the black in the hairs is diluted but not the red. The legs, tail and mane are all diluted as above since these are all black on a bay pony. Some times the bay pony with a mushroom allele are very red in colour and are confused with chestnut ponies with a flaxen mane and tail….The mushroom gene has no effect on chestnut ponies, but they can carry the gene hidden… The gene is dominant therefore only one allele is needed to express the colour. The problem is that since the gene has not yet been mapped there is no way of testing whether a pony is carrying the gene or not.
The above information is accredited to :- Anna Gamsgaard Frederiksen……….. to whom www.shetlandponyscotland.com is grateful for permission to reproduce.
A BASIC SUMMARY OF COLOUR DEFINITIONS
Black throughout, other than small white markings.
Reddish brown colour, includes, golden, liver & mahogany.
Light reddish brown to very dark brown with black mane, tail and lower legs.
White/grey or mixed dark and white coat.
A dark coloured coat with lighter rings of grey hairs scattered throughout.
White/grey coat with dark flicks throughout.
Tan Coat (yellow dun) with black or dark mane, tail, legs and dorsal stripe. (Blue dun) black/grey coat giving the appearance of blue with black or darker grey mane, tail, legs and dorsal stripe.
Red Roan, chestnut coat with white hairs, head, chestnut or with less white hairs than body. Blue roan, black coat with white hairs, head, black or with less white hairs than body.
White coat with large patches of any other colour except black.
White coat with large patches of black.
Golden yellow or tan coat with blond mane and tail.
OTHER DISTCRIPTIVE TERMS
A continuous black or dark stripe going from the neck along the back to the tail. Sometimes called an eel-stripe.
A white mark on forehead
A white mark on the forehead between the eyes and extending down the front of the face
A light/blond mane and tail of a chestnut
A small white mark on the nose
An oatmeal coloured muzzle