Color Genetics

Believe it or not there are only two base coat colors. Black and Red (also known as chestnut or sorrel). All other colors are modifications of these two colors… really!

SORREL or CHESTNUT?

s_feeding_grainThey both mean red and people disagree on the differences. Some breeds only recognize one color term, and not the other. Some folks think that Chestnut is an English rider’s term and Sorrel a Western Rider’s term. Some say blonde “reds” are Chestnuts, while others say Red “reds” are chestnuts. Confused? Yeah me too! Just know if they say Chestnut or Sorrel it is a red-based horse. For most of us, the rest is semantics.

Black is pretty black and white. Well really, it’s JUST black!s_friesen_mare_filly

Okay, a little Genetics 101: All chromosomes come in pairs and when a male and a female mate, the offspring gets one of the two chromosomes from each parent. Homozygous means that both chromosomes are the same, in layman’s terms; “what you see is what you get!”. Heterozygous means they are not. Still with me? Good!

How that works here is pretty simple:

Back to horses – Red is a recessive gene and can only be expressed when homozygous meaning both chromosomes are the same, in this case: ee. Black is dominant and will show up as either Ee (heterozygous) or EE (homozygous).

All things being equal (which works great on paper!) this is what you get when pairing animals with these colors:

BREEDING GENETICS COLORS & PERCENTAGES
Red/Red ee/ee Red ee 100%
Black/Red EE/ee Black Ee 100%
Black/Red Ee/ee Red ee 50% Black Ee 50%

 

But what about all the OTHER colors?

There are many modifiers out there, and right now we are only going to discuss a few. I wouldn’t want your head spinning like a top. So hang on, ’cause here we go…

BAY

bay_arabian1I’ll confess, as a kid I thought you bred a black mare to a chestnut stallion and you got a bay. Sometimes that’s even true, but not for the reasons my childlike mind was thinking. You see a Bay is really Black (Yeah, take a moment to wrap your brain around that one… it took me a few too!) I bet you are thinking it should be a Red horse modified with black points (legs, mane and tail). I did too, don’t feel bad! But when you understand the genetics of it, it makes more sense. The gene for getting black “RESTRICTED” to the points is called Agouti. And since there are only 2 base colors, when black is restricted the only other color that can show up is red. Makes more sense now, huh? Since there is no black on a red horse, it doesn’t show up… but it can still be there. Agouti is written aa when it’s not there, Aa showing up (just like black did with Ee) and is heterozygous and AA is homozygous.

As I mentioned, a red horse can carry the Agouti gene can pass it on to their young. This means a black horse known to NOT carrying the Agouti gene (aa) can be bred to a red horse which carries the gene and creates a bay. See, I WAS right… sometimes! 😉

GREY and WHITE

s_grey_barnFor years we have been told that genetically there is no such thing as a white horse (or if one is born, it will die soon after birth from Lethal White Syndrome). Recent break-throughs in genetics have shown a few select individuals (The Camarillo White Horse, for example) that are indeed genetically white. They are rare, and far and few between. Most white horses are either grey or extreme expressions of pinto. Like Black and Agouti, Grey is dominant. No grey is shown as gg and any horse with Gg or GG will turn grey eventually and perhaps even white.

BUCKSKINS, CREMELLOS, PALOMINOS, PERLINOS and SMOKEY BLACK

CREAM GENE RED BLACK BAY
None cc Red Black Bay
Incomplete Cc Palomino Smokey Black Buckskin
Complete CC Cremello Smokey Cream Perlino

s_buckskin_cowboy
These colors are all dilutes caused by the Cream Gene. The cream gene is a little different from the ones we have discussed thus far, it is incompletely dominant. Let me explain:

palominoBuckskins, Palominos and Smokey Blacks are collectively referred to as Single Dilutes. Visually, Smokey Black is indistinguishable from a regular black horse. All the horses mentioned above except Cremello or Perlino, have dark skin and generally have dark eyes. Cremello or Perlino are collectively referred to as Double Dilutes and have pink skin and blue eyes. Both are a creamy white color, however, Perlinos sometimes have a strawberry blonde cast which is most notable in their manes and tails. For pictures and information about double dilutes and the American Quarter Horse Association, check out the Cremello and Perlino Educational Association.

For a more thorough explanation of equine genetics and to learn about duns, champagnes, and pintos, and others, check out: A Beginner’s Guide to Equine Color Genetics or Animal Genetics Incorporated (they have a color calculator) or take a look at UC Davis Veterinary Genetics Laboratory.