Coat Color and Genetics

This info gathered from http://users.tpg.com.au/choclab/cci/cci.htm

The genetics of coat color is quite straight forward when you have come to terms with some genetics terms and principles.

DOMINANT & RECESSIVE are terms used to describe genes.  In Labrador coat color there are two sets of gene pairs, and the dominant and recessive interplay of these genes will determine the color of the dogs coat.
 

Labrador Fact

There are really only two coat colors, Black and Brown.  The Yellow dog is not the result of a color gene, but rather the inability to Express a dark coat color.

Three principles

Firstly - A Dominant gene will determine the color of a dogs coat if it is present in the genetic make up, no matter what other gene is present. And so:
Secondly - A Recessive gene can only determine the color of a dogs coat when no Dominant gene is present.
Third - Genes come in PAIRS, where one part of the gene is inherited from the mother and the other from the father.
 

Two Labrador Gene Pairs

One gene pair will determine dark coat color (Black is dominant, Brown is recessive), and another pair are Expression genes: the abiliy to express a dark coat (Dominant) and the inability to express a dark coat (recessive).

All this information is better understood if we use a shorthand way to represent the two sets of gene pairs.

B - black coat color                          b - brown coat color

E - able to to express a dark coat    e - unable to express a dark coat

By convention, the dominant gene is shown in upper case, the recessive in lower.

A coat color gene looks like this:  BB or Bb or bb

An expression gene looks like this: EE or Ee or ee

The interplay between the dominance issue and the two gene pairs will determine the color of the dogs coat.

If a Black dog mates with a Yellow bitch, what color will the puppies be?
The answer depends on the genes each parent carries.
The way the genes can be passed on is written out following a particular pattern.
First the parents genes are written with an x between to indicate a "cross" breeding.
eg. BbEE x BBee
Second: The genes the parents can pass on is written out into two tables.
eg. Taking the example above
 

Parent 1

 

Parent 2

  B b     B B
E BE bE   e Be Be
E BE bE   e Be Be


Note that the coat color genes are put in the top row of the table, and the expression genes are put into the side columns.
The results of this table give us all of the possible genes these two parents can pass on, and with this information, we can create another table to show us all of the types of puppies that could be produced.
All the Genes available from the first Parent are written in the top row, and the all the genes available from the second Parent are written down the column.

 

Parent 1 - Black (BbEE)

      BE BE bE bE

P
a
r
e
n
t

2


Y
e
l
l
o
w



B
B
e
e

Be

Be

Be

Be



So in this mating of a Black dog to a Yellow bitch, (BbEE x BBee) the only color puppy produced is Black.
This result comes about because, the Black dog has dominant Expresion genes, (although he carries a gene for chocolate), and the Yellow bitch carries two dominant color genes.
In this instance, half of the pups that could be produced would be Black carrying the ability to pass on yellow, and the other half would be Black, carrying both chocolate and yellow.
This 1/2 and 1/2 mix is the genetic probability.
 

All Pairings

Chocolate to Black Pairings

bbEE x BbEE will give the probability of 1/2 chocolate & 1/2 black.
bbEE x BbEe will give the probability of 1/2 chocolate & 1/2 black.
bbEe x BbEE will give the probability of 1/2 chocolate & 1/2 black.
bbEe x BbEe will give the probability of 3/8 chocolate, 1/4 yellow, 3/8 black (a rainbow litter).

Black to Black Pairings

How do two black dogs produce chocolate puppies? Both must be carrying a chocolate gene.
BbEE x BbEE will give the probability of 1/4 chocolate.
BbEE x BbEe will give the probability of 1/4 chocolate.
BbEe x BbEe will give the probability of 1/8 chocolate, 2/8 yellow, 5/8 black (a rainbow litter).

Yellow to Black Pairings

Bbee x BbEE will give the probability of 1/4 chocolate & 3/4 black.
Bbee x BbEe will give the probability of 1/8 chocolate & 3/8 black & 1/2 Yellow (a rainbow litter).
bbee x BbEE will give the probability of 1/2 chocolate & 1/2 black.
bbee x BbEe will give the probability of 1/4 chocolate, 1/2 yellow, 1/4 black (a rainbow litter).

Chocolate to Chocolate Pairings

bbEE x bbEE will give 100% chocolate puppies.
bbEE x bbEe will give 100% chocolate puppies. One half will carry yellow.
bbEe x bbEe will give the probability of 3/4 chocolate pups, and 1/4 pale yellow pups.

Chocolate to Yellow Pairings

bbEE x Bbee will give the probability of 1/2 chocolate & 1/2 black.
bbEE x bbee will give 100% chocolate.
bbEe x Bbee will give the probability of 1/4 chocolate, 1/2 yellow, 1/4 black (a rainbow litter).
bbEe x bbee will give the probability of 1/2 chocolate, 1/2 yellow with a brown nose.

(Yellow to Yellow will only ever produce yellow.)

All dogs with these genetics will look like this:
 BBEE BbEE BBEe BbEe

All dogs with these genetics will look like this:

 bbEE bbEe

All dogs with these genetics will look like this:

 BBee Bbee

All dogs of mine with these genetics will look like this:

 bbee