Category Archives: Horses

Color Genetics 101 (Part 1)

BASE COATS and MODIFIERS

I wrote this page a long time ago and thought I would share it with you. Most of you in the Horse World will be familiar with this information already, but it’s still a good primer. I will expand on it later in future posts.


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 — Sometimes it’s the other way around. 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 (EE for example), in layman’s terms; “what you see is what you get!”. Heterozygous means they are not (Ee). 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  Black
Red/Red ee/ee  100%
Black/Red EE/ee 100%
Black/Red Ee/ee 50% 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 is dominate (just like black is with Ee) and is heterozygous and AA is homozygous.

As I mentioned, a red horse can carry the Agouti gene and can pass it on to their young. This means a black horse known to NOT carry 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 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, PALOMINOS, SMOKEY BLACK, PERLINOS, CREMELLOS, and SMOKEY CREAM

s_buckskin_cowboyThese 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 in most breeds. For reasons not yet known, it is more noticeable in miniatures horses. More brown. Single dilutes have dark skin and generally have dark eyes.

Cremello, Smokey Cream and Perlino are collectively referred to as Double Dilutes and have pink skin and blue eyes. They are a creamy white color, however, Perlinos  and Smokey Creams sometimes have a strawberry blonde cast which is most notable in their manes and tails.

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

I would like to thank Jessica Zamboni of Cheyaut Ranch for fact checking. She is the wonderful friend who gave me my dog Gidget. Right now I live vicariously through her! Check out her page to see her Miniature and Icelandic Horses, as well as other assorted critters.

Horse Genetics Calculator

Next up: Pintos

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