Color II - Color Genetics in the Andalusian Horse - Bays, Blacks and Chestnuts

by Donna DeYoung Copyright 2002 © Skyhorse Kingdom

An article about color genetics of bay, black, and chestnut.

The dominant A (restrictor gene)  limits black to mane and tail. A black horse is a horse that has black not limited to the mane and tail, the whole body is black and his genotype would be "aa".

The dominant E (black hair) gene allows black to be present in the hair. When dominant E is not present, the horse will be ee (chestnut result). The horse will have black skin but the hair will be red because there is no black melanin in it.

The A (restrictor gene) and E (black hair gene) interact together.

If a horse has at least one copy of the dominant E (black hair gene) he is EE or Ee. The E (black hair gene) will result in the horse being black or bay with potential to pass on bay and black.

If a horse is ee (recessive gene and chestnut result), the horse has black skin, but no black hairs because he did not get an E (black hair gene). He is a chestnut with no potential to pass on black or bay.

When a horse has the A (restrictor gene), the A (restrictor gene) is dominant and limits the black E gene to the points (ie black mane and tail). So if a horse inherits EE or Ee as above and also an A, he will be bay.

The absense of A (restrictor gene), or aa (black result), allows the black to be over the entire body. So a horse that inherits an E and also the aa will be solid black.

However, if a horse is not bay or black (he is ee and chestnut), the A (black restrictor) gene or aa (black all over the body) gene does not affect him.

So, to sum up: A horse with EE or Ee is a bay or black; ee is a chestnut; AA or Aa has the restrictor gene. So, before studying this table...ask yourself...can a bay produce chestnut or black? Yes, it depends on the genotype. Can a black produce chestnut or bay? Yes, it depends on the genotype. Can a chestnut produce bay or black? Yes, it depends on the genotype.


 

Genotype

Phenotype (what the horse looks like)

Can he produce chestnut? (is"e” present?)

Can he produce black? (is “a” present?)

Can he produce bay? (is “E” present?)

EEAA

Bay

no

no

yes

EeAA

Bay

yes

no

yes

EEAa

Bay

no

yes

yes

EeAa

Bay

yes

yes

yes

Eeaa

Black

yes

yes

yes

EEaa

Black

no

yes

yes

eeAA

Chestnut

yes

no

yes (e is recessive)

eeAa

Chestnut

yes

yes

yes (e is recessive)

eeaa

Chestnut

yes

yes

yes (e is recessive)

How to use these charts:

Each chart depicts a phenotype of horse bred to another phenotype of horse. For example, all other colors excluded, when you breed bays to bays you end up with mostly bays, some chestnuts and very few blacks.

The first and second columns are all the different genotype possibilities. The first column is then crossed with the second column. The results are shown in genotype as text. The color of the row shows the resulting phenotype. The results were calculated using Punnett squares (see Genetics I for an example of how Punnet Squares work).

If you were breeding a bay horse that in the past had produced black his genotype would have to be E_Aa (the "a" allows for the color black to occur).  If you bred two such horses together you would get the results as shown below in row # 7 which is about 1/2 bays, and 1/8 chestnut and 1/8 black ("aa").

Bay E_A_ bred to Bay E_A (1/80 black; 7/80 chestnut; 13/20 bay)

EEAA

EEAA

 

EEAA

EEAA

EeAA

EEAA

EeAA

EEAA

EEAa

EEAA

EEAa

EEAA

EeAa

EEAA

EEAa

EeAA

EeAa

EEAa

EeAA

EEAA

EeAA

EeAa

EEAa

EeAa

EEAA

EeAa

EeAA

EeAa

EeAa

EEAA

EEAa

EeAA

EeAa

eeAA

Eeaa

EeAa

EeAA

EEAA

EEAa

EeAA

eeAA

eeAa

EeAA

EeAa

EEAA

EEAa

EeAA

EeAa

eeAA

eeAa

EeAA

EeAA

EEAA

EeAA

EeAA

eeAA

Bay E_A_ bred to Black E_aa (3/64 chestnut; 19/64 black; 21/32 bay)

EEAA

EEaa

 

EEAa

EEAA

Eeaa

EEAa

EeAa

EEAa

Eeaa

EEAa

EeAa

EEaa

Eeaa

EeAA

EEaa

EEAa

EEaa

EeAA

Eeaa

EEAa

EeAa

EEaa

 

Eeaa

 

EeAa

EEaa

EEAa

EeAa

EEaa

Eeaa

EeAa

Eeaa

EEAa

EeAa

EEaa

Eeaa

eeaa

EeAA

Eeaa

EEAa

EeAa

eeAa

Black E_aa bred to Black E_aa (1/12 chestnut; 1/4 bay; 3/4 black)

Eeaa

EEaa

 

EEaa

Eeaa

EEaa

EEaa

EEaa

Eeaa

Eeaa

EEaa

Eeaa

Eeaa

eeaa

Chestnut ee__ bred to Chestnut ee__ (1/14 black; 13/14 chestnut)

eeAA

eeAA

 

eeAa

eeAA

eeAa

eeAA

eeAa

eeAA

eeaa

eeAa

eeAa

eeAa

eeAA

eeAa

eeaa

eeaa

eeaa

eeaa

eeAa

eeaa

eeAa

eeaa

eeaa

Eeaa

Eeaa

eeaa

Chestnut ee__ bred to Black E_aa (1/10 black; 3/10 chestnut; 1/2 bay)

eeAA

EEaa

 

EeAa

eeAA

Eeaa

 

EeAa

eeAa

eeAa

Eeaa

 

EeAa

Eeaa

eeAa

eeaa

eeAa

EEaa

 

EeAa

Eeaa

eeaa

EEaa

 

Eeaa

Chestnut ee__ bred to Bay E_A_ (3/48 black;1/6 chestnut; 33/48 bay)

eeaa

EEAA

 

EeAa

eeAA

EEAA

EeAA

eeAA

EEAa

EeAA

EeAa

eeAA

EeAA

EeAA

EeAa

eeAA

EeAa

EeAA

EeAa

eeAA 

eeAa 

eeAa

EeAa

EeAA

EeAa

Eeaa

eeAA

eeAa

eeAa

eeaa

eeaa

EeAa

EeAa

Eeaa

eeAa

eeaa

eeAa

EeAA

EeAA

EeAa

eeAA

eeAa

eeaa

EeAA

EeAa

eeAa

eeAa

EEAA

EeAa

eeAA

eeAa

EEAa

EeAA

EeAa

Eeae

eeaa

EEAa

EeAa

EeAa

EeAa

EeAa

Eeaa

Eeaa

Eeaa

Eeaa

 

 

Templates in Time