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Understanding gene dilution and coat pattern!

We understand that the dilution of genes and the presence of the tobiano gene can be slightly confusing so we have tried to compose a guide to simplify the basics!

Colour Classifications

                                                 
Grey - a dominant grey gene combined with a recessive gene for colour (bay/black or chestnut)  N.B. A grey horse will always have a 50% chance of producing grey offspring.

 

   
Bay/chestnut and black – no dilute gene present therefore classified for this purpose as solid.

 

Buckskin (a horse with yellow and black body pars) – this is the bay gene with a single dilute gene

   

 

Palomino (yellow horses with no black points) – this is the chestnut gene with a single dilute gene

   
Smokey black (Dunhill Pursuit) – this is the black gene with a single dilute gene

 

   
Cremello (Crowns Wonder Pearl) (cream coloured horses with blue eyes and their manes and tails are nearly white))– this is the chestnut gene with double dilute

 

Perlino (Dunhill Desert Storm)  (as the cremello but these horses retain some pale colour in the mane, tail and lower leg, the can look “dirty”)– this is the bay gene with a double dilute

Tobiano – a combination of pattern (Tobiano) and a solid colour i.e. skewbald

   

Dilute Tobiano – a combination of colour and a dilute colour i.e. buckskin and white

In a nutshell how do you classify your mare:

Dominant Grey – Grey.

Solid (nn) – Bay, Black, Chestnut.

Single dilute( nCr)Palomino, Buckskin, Smokey Black.  

Double Dilute (CrCr)  - Cremello, Perlino

The simplest genetic colour of all  horses can be described as either "red" or "non-red", depending on whether a gene known as the "Extension" gene is present . When no other genes are active, a "red" horse is chestnut.  Black coat colour occurs when the Extension gene is present, but no other genes are acting on coat color.The Agouti gene can be recognized only in "non-red" horses; it determines whether black colour is uniform, creating a black horse, or limited to the points of the body, creating a bay horse.

It is important to bear in mind that both our double dilute stallions, Crowns Wonder Pearl and Dunhill Desert Storm are both homozygous for the Agouti gene therefore they can not produce a smokey black.

Terms you need to know

Heterozygous – 50% chance of passing on the gene

Homozygous – 100% chance of passing on the gene

 

Homozygous Tobiano – T/T

Heterozygous Tobiano  - n/T

 

So what does this mean if you cover your mare with a stallion of one of the above colours?

 

Grey – If you choose to cover your mare with a grey stallion or vice versa you will have a minimum 50% chance of the resulting offspring being grey.  This likelihood increases if your mare is grey or if indeed the stallion or the mare are homozygous for the grey gene.

The various colour combinations for solid mares when covered by either a single or a double dilute stallion - 

In the case of using a double dilute stallion the cream gene is certain to be passed and therefore on a solid mare or a single dilute mare the resulting foal with definitely show the dilution and vice versa.

If you are using a single dilute stallion on a solid mare you have a 25% chance of the cream gene being passed on and vice versa.

If you are using both a single dilute stallion and a single dilute mare the possibilities are 33.33% double dilute, 33.33% single dilute and 33.33% solid

The cremello dilution guarantees to produce palomino from chestnut.  In the case of the other dilutions the appearance of chestnut, bay and black will have an impact on the colour.

Now to deal with tobiano!

If you are covering your solid coloured mare with a heterozygous tobiano stallion and vice versa  you will have a 25% chance of the resulting offspring being coloured. 

 

If both your mare and your choosen stallion carry the tobiano gene and are both heterozygous then you have 3 possibilities, a 33.33% chance of a) solid b) homozygous tobiano c) heterozygous tobiano.

 

If you are covering a solid coloured mare with a homozygous stallion and vice versa then you are guaranteed a coloured foal. 

 

If both your mare and your choosen stallion are homozygous for tobiano then the resulting foal is certain to be coloured.

 

If you are dealing with a dilute tobiano (Multicolor II) the possibilities alter again! 

A dilute tobiano carries both the dilute gene and the tobiano gene so either gene, both genes or none of the genes may be passed on!!

So if we look at a heterozygous dilute tobiano with a bay mare, here is an example of the colour of the offspring that could be produced.

 

Offspring Color Probability

21.97% - Buckskin Tobiano, Buckskin, Bay Tobiano and bay

1.56% - Palomino Tobiano, Palomino, Chestnut Tobiano and Chestnut

1.46% - Smokey black Tobiano, Smokey black, black and black tobiano

 

A single dilute mare:

Offspring Color Probability

21.97% - Buckskin and Buckskin Tobiano

10.99% - Bay Tobiano, Perlino Tobiano, Perlino and Bay

1.56% - Palomino Tobiano, Palomino and Smokey Black Tobiano

1.46% - Smokey Black

0.78% - Cremello Tobiano, Chestnut and Cremello

 

Therefore when dealing with dilute tobianos you do have the possibility (albeit very small) of producing a solid coloured foal

With all these combinations there are many results and a great website to play about with colour genetics is

http://www.animalgenetics.us/CCalculator1.asp

This article has been done to the best of our ablility, plese let us know if you see any incorrect information. 

We do hope it helps

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