a brief essay
© Kim Middel 1995
A very special colour: ljósmoldótt, ljósfext.
The mare Hulda Hnöll frá Torfunesi
Colour inheritance in horses is not half as difficult as it seems: there is a very logical explanation to almost anything you see. When one looks at a very colourful species of horses such as the Icelandic horse the range of colours and colour combinations seems endless and impossible to tag names onto; in fact, it is only a matter of sorting out gene patterns.
First of all, it is necessary to know that all colours are based on the basic colours chestnut, bay and black. These three colours are based on the presence of the following genes:
E - causes black and brown pigment, eumelanin, to be formed when present in dominant form.
A - causes red and yellow pigment on top of black (EE or Ee), phæomelanin to be formed when present in dominant form.
These are fully dominant, i.e. only one of the alleles has to be dominant to effect full forming of the pigment involved. Thus:
chestnut; if a horse has a A. ee genotype, for instance if it is born out of a bay parent and a chestnut parent, its phenotype will still be chestnut, for A only interferes with E, not with e! This accounts for the fact that out of a chestnut and a black horse a bay foal can be born.
Colours caused by the Ccr-locus
Son of Buck TWH
Let us first look at what the C-locus does. The C-locus has three alleles:
two dominant ones and a recessive one. The C-allele does nothing, the Ccr-allele
effects dilution of colours. Ccr is not fully dominant: its influence on
the basic colours is more intense when homozygously dominant than when
heterozygously dominant. It cannot overrule the strength of C completely.
Longview Takes No Chances TWH
The D-locus (D for dun) causes dun colours when present in dominant form: the colour becomes lighter and a dorsal stripe to appear on the back; perhaps also wild stripes on the legs and a stripe crossing from one shoulder over the back to another. Legs and head are always of darker colour than the rest of the body. The dominancy is full; homozygous dominant alleles are denotated as DD, heterozygous dominant alleles as Dd.
In Amrican terminology there are more than one way for describing dun horses, e.g. apricot dun (red dun with orange body and red mane, tail and eel stripe), golden dun (either light red dun or palomino dun), cream dun (dun palomino) and silver dun (light blue dun). Mind you these are only terms for fenotypes, not for genotypes!
The P-locus causes skew- or piebald (Am.: tobiano) spotted patterns;
it is a dominant gene and the most common of the genes that cause spotting.
The white fields on the horse are mainly on the shoulders, back and flanks.
White fields on the back will also interrupt dorsal stripes if present.
Thrymur frá Geirshlíd
black silver dapple
The F-locus causes what is called white-headed paint or splashed white
horses. It seems to colour the parts of the horse white that would probably
have been coloured in a normal tobiano pattern: The belly, the neck and,
most important, the head. The colour only seems to occur in species from
Northern Europe (F for Finnish paint, since it was first found in Finland).
It works when homozygous recessive present. Therefore, out of two normally
coloured looking parents, a whiteheaded paint can be born.
The O-locus causes sabino paint colouring. It is best seen in Shire horses: unsharp, mottled white big spots on the belly and large white "boots" covering the legs. The white fields have not a very distinguished end butget diluted into the coloured fields. Even the sheer presence of the completely white legs is enough to spot a sabino paint. The presence of white can vary from one single little white spot to a white horse with vague coloured spots coming through the white. It is fully dominant.
aa E. O. = sabino paint black (Shire)
The Om-locus is a mutant form of the O-locus, causing overo spot- ting: a coloured back, white fields on the sides marked by frea- kishly coloured fields on the edges. This is a common sort of paint in American horses. It works in homozygous recessive form.
A. E. CCcr omom = buckskin overo paint
Generator's Pushin' Blue THW
A. E. CCcr R. = buckskin roan
The G-locus is fully dominant and causes decoloration of any colour
unto dapple grey or white in the first 3 to 7 years of its life.
A. E. Z. P. G. = grey, born silver dapple bay skewbald
The W-locus (lethal white)
The W-locus causes white colouring with blue eyes in heterozygous dominant
form; these horses are not albino's for albino
aa E. W. = White, born black
Fairwind's Standing Ovation Tiger Horse
white body, coloured spots everywhere except in the tail area
least: a mutant of the W-locus, Wap (ap for appaloosa), and the S-locus (S for spotting). The dominant Wap-allele will cause both white colouring and spotting, but they will only come out well if the horses is homozygous recessive for S. If either one of them is missing, no appaloosa spotting will come out. Thus:
A. E. Wap. ss = appaloosa, white with brown spots.
On top of this, there are five more loci that influence and af- fect the appaloosa patterns:
* the Sl-locus (Sl for silver);
If two or three of the first mentioned loci work, with or without Eap
or Rap, so-called blankets of different size and colour
Do you still get it? I hope you do. Now then, to make it interesting (so you can predict what colours of foals your mare will be able to give birth to next year or what colours you sire can produce with which dams), let us now look at some crossing schemes. These have all been derived from real examples.
Since a foal receives one gene from each parent, their gene pairs have been split so when the single gene from the male meets the single gene of the female they will again form a pair. It is therefore that pairs of alleles are split when you want to make a crossing scheme; you have to take all the possibilities of allele-combinations.
For example, a bay horse which has a AaEE genotype can give the following combinations after splitting its pair of genes: AE, AE, aE and aE.
The red dun (aa ee Dd) sire Gustur 754 frá Hrafnkelsstöðum
and the piebald dam Skjóna frá Ólafsvöllum (aa
Ee Pp) produced a mouse dun foal called Björk. Since only the father
carried the D-locus, and only the mother carried E and P, Björk was
heterozygous for nearly all loci: aa Ee Dd Pp.
There was a 1 in 8 chance of this colour.
The palomino dun mare Leira (aa ee CCcr Dd) produced three offspring, two of which buckskin and one palomino. Leira was born out of a palomino stallion, Amor (Lýsingsson) 793 frá Ásgeirsbrekku, and a dun mare. She therefore had only one D-allele which she did not pass on to these three foals. They were born out of a bay, a black and a chestnut stallion. Let us look how great the odds were for the colour of the first foal born.
The first foal, a buckskin mare named Drottning, was by Jarpur fá
Sandhólaferju, who is supposedly AaEe.
Icelandic and Dutch names for colour patterns
Both the Icelandic and Dutch language have a wide range of names for colour patterns in horses. Here's a scheme of their variety:
ENGLISH ICELANDIC DUTCH black svartur/brúnn zwart bay jarpur bruin chestnut rauður vos smoky mosóttur/glóbrúnn smoky buckskin moldóttur valk palomino leirljós isabel silversmoky glóbrúnn/mórauður zilversmoky perlino hvítingur perlino cremello hvítingur cremello blue/mouse dun móálóttur wildkleur zwart yellow dun bleikálóttur wildkleur bruin red dun (fífill-)bleikur wildkleur vos/leemvos smoky dun - wildkleur smoky buckskin dun bleikmoldóttur wildkleur valk palomino dun bleikleirljós wildkleur isabel grey grár grijs/schimmel roan -litföróttur -schimmel * e.g. red roan rauðlitföróttur roodschimmel pie-/skewbald -skjóttur -bont *e.g. buckskin skewbald moldskjóttur valkbont Finnish paint/ kápóttur witkopbont splashed white sléttuskjóttur silver dapple black móvindóttur zilverappelzwart silver dapple bay rauðvindóttur zilverappelbruin
but:silver dapple mouse vindmóalóttur zilverappel wildkleur zwart
silver dapple grey vindgrár zilverappel grijs
Post scriptumI really hope you have enjoyed this bit of genetics and that the story has been clear and will be happy to receive comments or questions.
We intend to get similar articles online, so feedback at this stage
is very important!
PRINT Version Takes a while to open, be patient
WebUse Copyright Gaited Horses
All rights reserved.
No material from this website may be copied or reused without
specific written permission from Gaited Horses.
and THEN Fill out form below.
OR Fill out Form Below and mail check.
Check made out to:
P.O. Box 54
Waynesboro, Georgia 30830
BACK to List of Articles