Colour Genetics in Spaelsau

By Ottar Endresen 

In this article I will give a short introduction on how the main colours, white, black and brown are inherited in spaelsau and spaelsau (spel-sheep) variants like Norwegian Feral Sheep, Icelandic, North Ronaldsay etc.

Genes

Genes control each of the sheep’s character. The genes are joined in pairs. The offspring inherits one of the genes from the father and the other from the mother.The genes for colour and colour-patterns are related to special locations on the chromosomes. Usually each gene is named by a capital letter indicating the location in the chromosome, and with a small letter or + to indicate the specific character which is possible in this gene. A + tells that it is considered to be the original character. The letter w can indicate white colour etc.

Black or brown (moorit)?   (B-locus)


Black or brown.

However, the gene controlling whether a sheep is going to be black or brown is located in the B-locus on one of the sheep’s pair of chromosomes.

Black is considered to be the original colour, and hence has +, while brown has a small letter b in the code. We can now put together the following code:   

B+  Indicates black colour. B+ is dominant to Bb.  
Bb Indicates brown colour. Bb is recessive to B+.
A sheep can have the following combinations of genes in the B locus:
B+B+ The sheep is black. It is homozygous for black colour. This sheep will always carry black lambs, even mated to a brown ram. (White colour is so far excluded)   
B+Bb The sheep is black, because the gene for black is dominant. But the gene for brown is hidden, and the sheep is able to give brown lambs if mated with a similar black ram (B+Bb) or a brown ram (BbBb).  
BbBb The sheep is brown, because it is homozygous for brown (moorit) colour. It will always give brown lambs when mated with a brown ram. If crossed with a black  ram (B+B+) it will give black lambs. Mated with a black ram (B+Bb) it will give fifty-fifty of black and brown lambs.

When crossing a single character there will always be four possibilities, because each pair of genes are divided and appear as single genes in the gametes.

Starting with a pure black and/or pure brown ewes and rams, we will have these following possibilities: 

Examples. 


- A mild mix.

a.

A sheep breeder has only pure black sheep (B+B+) and wishes to get in brown animals in his flock. He buys a brown ram to mate all the ewes.  
In the first generation, all lambs will turn out black, but they will also have a hidden gene for brown colour. If you cross all these lambs with a brown ram it will give a second generation where fifty percent of the lambs become brown.  
If
mating lambs of first generation mutually, 25 percent of the second generation lamb will be brown, the rest black.
 

b.

A sheep breeder has only brown sheep (bbBb), and wishes to get in black colour.  
He buys a black ram. But the ram can be B+B+ or B+Bb.
 
In the first case, all lambs in the first generation will be black. In the second case (B+Bb), fifty percent of the first generation lambs will be black.

c.

Or he, who had only white sheep and had bought a black ram to get in colours. But then all the lambs turned out white! Just according to the scheme. In the next generation the colours will appear.   

Genes dominating black and brown – colour-patterns.   (A-locus)

White colour, solid colour (without tan under coat), grey (blue) or tan colour and mouflon-pattern are located at another location on the chromosome, called A-locus. As mentioned before each gene is normally named with a capital letter for the  location, the locus, and a small letter or + for the character. 

We can now put together the following codes:   

A+  mouflon-pattern
Aa solid colour (both outer and under coat fibers are black or brown)  
Ab badgerface.  
Aw white.  
Ag grey (tan) under coat in black or brown outer coat.

According to this, a black sheep will have the pair of genes AaAa in addition to B+B+ or B+Bb. 

A brown sheep will also have the genes AaAa in addition to BbBb. 

A grey sheep (blue or tan) will have the AaAg genes. 

A sheep with double genes for tan colour, AgAG turns fairly tan as adult, nearly white, but with a grey head and grey/brown legs. 


 What kind of genes do we hide?

In a way the A characters add a pattern to the basic colours, black or brown. The Aw gene is dominant to all other characters in the A-locus. Consequently the following pair of genes will give white sheep: 

AwAw,  AwA+,  AwAa,  AwAg  etc. 

According to the list above, a white sheep can have the following gene-combinations at the A-loci: 

AwAw The gene for white colour is homozygous. Always carrying white lambs.  
AwA+  Will be able to give white and mouflon-coloured lambs.  
AwAa Will be able to give white and full-coloured lambs.  
AwAb Will be able to give white and badgerfaced lambs.  
AwAg Will be able to give white lambs and lambs with tan under coat.

      


left, A+Ag BbBb right, A+Aa BbBb

Mouflon-pattern, A+ is dominating Aa and Ag. Which means that the following pairs of genes will give mouflon-coloured sheep: 

A+A+,  A+Aa and A+Ag. 

Specially for mouflon-coloured sheep:   

A+A+ The gene for mouflon-pattern is homozygous. Give always mouflon-pattern.   
A+Aa Will be able to give mouflon-colour and solid-coloured lambs.
A+Ag Will be able to give mouflon-coloured lambs, and lambs with tan under coat.

Whether the basic colour in the mouflon-coloured sheep will be tan (Ag) or dark (Aa) depends on the genetic makeup of the other parent. 


   A+Aa B+Bb The ewe has inherited the A+ gene from her white mother. Her father was solid brown                          

 This show that two white sheep can have coloured offspring, while two coloured sheep can’t get white lambs. The character for white can’t be hidden, because it isdominant to the solid-colour gene.

Likewise, two mouflon-coloured sheep can have offspring, which is not mouflon-coloured, while two coloured sheep can’t get mouflon-coloured offspring. On the other hand, mouflon-coloured lambs can occur from two white parents, because Aw dominates A+. 

Markings and horns


A+Aa BbBb with white markings in the face.

The sheep can also have bigger or smaller distinct markings at different places on the body. This we call “spots”. Most prevalent are spots in the face, on the legs and on the tail.

Markings are unsymmetrical contrary to “patterns” which are always symmetrical. I have no knowledge concerning genetics on markings and horns. Therefore I challenge others to learn us about this.  

Good luck with the colour-composition of your spaelsau-flock! 

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SHEEP-ISLE recommends for further reading the pioneer – and still unsurpassed – work on genetics written by dr. Stefan Adalsteinsson:

 

Colour inheritance in Icelandic Sheep

J. Agric. Res. Iceland 2, 1-135 1970  

Stefan Adalsteinsson on Sheep-Isle (Shetland Sheep) 

Translation:  Sheep-Isle

Photos: O. Endresen

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About Ottar Endresen

Mr. Endresen is a typical Norwegian West Coast Sheepbreeder with his spaelsau flock on summer-grazing in the Sirdal mountains. He is also a theorist, well up in the subject. He is even the driving force in the work of preserving the old spaelsau-variant, Old Norwegian Spaelsau.
All these qualifications makes him self-evident as permanent guest writer on Sheep-Isle!

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