Horse Color Genetics that YOU can understand

Genetics is a scientific theory - although the geneticists may present the information as fact - it is not. In most cases the theories are tested and accepted as true - but there is no way to really prove them, in most cases a theory can only be disproved. Although unlikely, the scientists could be wrong.

Next, to understand genetics and how color is passed from the parents to the foal, you must understand and accept that in most cases a parent passing or not passing a specific gene to a foal is a 50/50 shot. But, just like tossing a coin - the odds each time a foal is conceived it is 50/50 odds again. Just because a stallion and mare produced a certain color baby, the odds of them doing it again is not any better or any worse than it was before they produced the first one.

THE GREY GENE
Grey is one of the simplest genes to understand. Grey is a dominant gene and therefore if a horse has the grey gene it is ALWAYS expressed (a horse that has the grey gene will always turn grey). Also, the grey gene is not masked by or altered by any other color (although a palomino that turns grey is a different color than a black that turns grey - they are both grey horses). A horse is either Grey or Not Grey (signified by G(Grey) or g(not grey)). Each horses carries two grey genes - these can be one of the following combinations:

GG - Homozygous Grey (all foals will be grey as they will always pass a grey gene onto their foal)

Gg - Heterozygous Grey (50 percent of their foals should be grey - although it may take hundreds of foals before the percentage ever comes out to 50/50)

gg - Non grey (this horse can not pass a grey gene onto its foals)

If a neither parent is grey, they can never produce a grey foal. If both of the parents are grey, they may or may not produce a grey foal. Each parent gives the foal a Grey gene (either G or g) and the foal color is produced from that.

This Example is a true life example (my mare) of a grey mare that has produced 5 foals and only 1 was grey.  When breeding a heterozygous grey dam and a non-grey sire  - you have the possibilities shown the following page. In this case (a heterozygous grey) there is no strong grey or weak grey - there is no scientific reason that the grey has only produced 1 grey out of 5 foals -- it is just luck. If you had a homozygous grey mare (a mare that carries 2 grey genes), then it would always produce a grey foal, regardless of the color of the sire.

We know that the mare is heterozygous, she does not always produce grey offspring so her grey genotype is Gg. The sire is not grey and therefore we know his grey genotype is gg 

When you combine the two you can get the offspring shown on the following page. Each parent contributes one gene to the offspring (and the gene contributed can be either of the two that the parents carry)


BREEDING HETEROZYOUS MARE TO NON GREY STALLION

Sire -- gg   Dam -- Gg

Sire can pass either the red g or the blue g onto his offspring
Dam can pass either the green G or the pink g onto her offspring

There are 4 possible combinations for foals from this sire and dam

1) gG Sire gave us the red g and Dam gave us the green G - 25%
2) gg Sire gave us the red g and Dam gave us the pink g - 25% 
3) gG Sire gave us the blue g and Dam gave us the green G - 25%
4) gg Sire gave us the blue g and Dam gave us the pink g - 25%

These are ALL the possible combinations of the grey gene from this dam and sire. This indicates that each time they they have an equal chance of producing any of the four combinations. 2 of the combinations show that the foal will be grey (indicated by the large green G - 1 and 3) and the other two show the foal would not be grey (2 and 4). 

From this chart you can see that the odds of this dam and sire having a grey foal is 50/50. Keep in mind that just because dam has not had a grey foal for 3 years the odds of her having a grey foal next year is still 50/50. Just like tossing a coin - just because it comes up heads 3 times doesn't mean that it will come up tails the next time. 


BREEDING TWO GREY HORSES

SIRE -- Gg MARE -- Gg

We are now going to cover breeding 2 grey horses together and what they will produce. The sire can pass either the red G or the blue g onto his offspring and the mare can pass either the green G or the pink g onto her offspring. Remember the large G indicates the GREY gene. There are 4 possible combinations for passing on the grey gene from this sire and mare.

1) GG The Sire gave us the red G and The mare gave us the green G - 25%
2) Gg The Sire gave us the red G and The mare gave us the pink g - 25% 
3) gG The Sire gave us the blue g and The mare gave us the green G - 25%
4) gg The Sire gave us the blue g and The mare gave us the pink g - 25%

This chart indicates that breeding 2 heterozygous grey horses would give you a 75% chance of getting a grey foal (1, 2 and 3) and 25% change of a non-grey foal (4). Note that # 1 has two G genes (grey genes) which means if you got this combination this horses would ALWAYS produce a grey foal. There is no evidence that a GG horse is more grey or greys earlier - but will always pass on the grey gene to it offspring as indicated on the following page.



BREEDING A HOMOZYGOUS GREY HORSE

SIRE -- GG MARE -- gg

In the example here we have a homozygous grey sire (this horse carries 2 grey genes and all offspring of this horse will be grey regardless of what he is bred too). The sire can pass either the red G or the blue G onto his offspring and the mare can pass either the green g or the pink g onto her offspring. Remember the large G indicates the GREY gene. There are 4 possible combinations for passing on the grey gene from this sire and mare.

1) Gg The Sire gave us the red G and The mare gave us the green g - 25%
2) Gg The Sire gave us the red G and The mare gave us the pink g - 25% 
3) Gg The Sire gave us the blue G and The mare gave us the green g - 25%
4) Gg The Sire gave us the blue G and The mare gave us the pink g - 25%

As indicated in the chart above there are still 4 combinations - but in every combination the sire has passed on one of his grey genes to the foal and therefore the foals have 100% chance of being grey. Note that if the mare had also had a grey gene the foals would still be grey - but 50% of them would have 2 grey genes instead of 1.


BREEDING TWO NON GREY HORSES

SIRE -- gg MARE -- gg

Since Grey is a dominant gene (always expressed if the horse has the gene) if you breed 2 non-grey horses you will never get a grey horse. In the following example we have 2 non-grey horses. I am going through this exercise just to show why you can not get a grey from 2 non-greys.

1) gg The Sire gave us the red g and The mare gave us the green g - 25%
2) gg The Sire gave us the red g and The mare gave us the pink g - 25% 
3) gg The Sire gave us the blue g and The mare gave us the green g - 25%
4) gg The Sire gave us the blue g and The mare gave us the pink g - 25%

As indicated in the chart above there are still 4 combinations - in every combination both the genes are non-grey and therefore 100% of the foals will be non-grey.

This discussion of the Grey gene carries over to all pure dominant genes (Roan, Champagne, Dun and so on). These are genes that are always dominant and will also be expressed (shown) if the horse carries the gene. Palomino is dominant to every color but black.

The recessive genes are much harder to trace and can typically only be recognized if two horses breed and have a foal that has 2 of the recessive genes -- for example the curly gene in foxtrotters can be recessive - it could show up at any time when breeding 2 non-curly horses. In this case each horse (the mare and the stallion) passed on the curly gene to their offspring and produced a curly horse.

DOMINANT GENES/CHAMPAGNE

The following four genes are dominant genes that are either ON or OFF - they have an effect on the color only if they are present. If they are absent they have no effect. 

G/g -- Grey/non-grey
Ch/ch -- Champagne/non-champagne
D/d -- Dun/non-dun
R/r -- Roan/non-roan
T/t -- Tobiano spotted/non-spotted

As you can see the Champagne gene is one of the genes that works very similar to the grey gene. If you go back and look at the grey genetics and plug Champagne in for each G(Grey gene) you would come up with the same percentages. In other words, breeding a Champagne horse to a non-champagne horse should give you 50% Champagnes. You can never get a Champagne foal by breeding 2 non-champagne horses and if you could find a homozygous champagne horse you would get 100% champagne foals. (Note: to have a chance of getting a homozygous champagne horse BOTH parents must be champagnes).

Example 1
Sire -- Champagne -- Ch/ch Mare -- non-champagne -- ch/ch

1) Chch - Sire passed on Ch, mare passed on ch (1st one) -- 25%
2) Chch - Sire passed on Ch, mare passed on ch (2nd one) -- 25%
3) chch - Sire passed on ch, mare passed on ch (1st) --25%
4) chch - Sire passed on ch, mare passed on ch (2nd) -- 25%

In this case you have a 50/50 chance of producing a champagne foal.

Example 2
Sire -- Champagne -- Ch/ch Mare - Champagne -- Ch/ch

1) ChCh - Sire passed on Ch, mare passed on Ch -- 25%
2) Chch - Sire passed on Ch, mare passed on ch -- 25%
3) chCh - Sire passed on ch, mare passed on Ch --25%
4) chch - Sire passed on ch, mare passed on ch -- 25%

In this case you have a 75% chance of producing a champagne foal (a 25% chance of producing a homozygous Champagne foal and 50% chance of producing a heterozygous champagne foal). The odds of getting a non-champagne is 25%. 

Example 3
Sire -- Homozygous Champagne -- Ch/Ch Mare - Champagne -- Ch/ch

5) ChCh - Sire passed on Ch, mare passed on Ch -- 25%
6) Chch - Sire passed on Ch, mare passed on ch -- 25%
7) ChCh - Sire passed on Ch, mare passed on Ch --25%
8) Chch - Sire passed on Ch, mare passed on ch -- 25%

In this example the sire is a homozygous champagne. He will always produce a champagne foals no matter what he is bred too. This example shows a Champagne mare and therefore the foals produced are 50% homozygous champagne and 50% heterozygous champagne.

Current documentation indicates that a homozygous Champagne would look very much like its heterozygous counterpart.  Unlike creams where a double dilute is obvious (cremello, perlino, smoky cream) with diluted coat color, pink skin and blue eyes.  It seems that a homozygous gold champagne looks pretty much like a heterozygous gold champagne.