Coat Color Genetics

(by Tina Porter Lakeway Kennel)

Have you ever wondered what color you next litter of puppies will be? Or why your two sable dogs produced a litter of black and tans?  It all has to do with genetics- specifically coat color genetics.

Just to make sure we are all starting out in the same spot, here is a quick refresher on basic Mendelian genetics.  If you already have a good grasp of genetics you might want to skip this part J

Trait: a feature or characteristic that is inherited.  It is usually represented by a letter. Example- coat length = L

Gene: the specific segment of DNA on a chromosome that codes for a particular trait. Example- gene for coat length is located on chromosome. 12.

Allele: version of the trait/gene.  Each allele is given a version of the letter assigned to a trait. Example- the gene for coat length has two alleles- one for the smooth coat (L), and one for plush coat (l).

Chromosomes:  “packets” of genes.  Dogs have 78 chromosomes, 38 pairs and two sex chromosomes (determine gender).  The paired chromosomes (sometimes called autosomes or homologous) contain the same Think of it in terms of a shoe store. They have 38 different pairs of shoes (chromosomes).  They are all different styles (different chromosome pairs carry different genes), but each pair have the same style (homologous chromosomes have the same genes).  This means you have 2 copies of a gene – one on the right shoe, and one on the left.  As you look closely at your pair of shoes you’ll notice they are not exactly the same – one is a righty, the other a lefty. (you have 2 copies of the gene, but maybe not the same alleles).  One of the shoe/chromosomes you inherited from the sire, the other from the dam.

Genotype- what alleles you have for a particular gene. Remember you have 2 alleles, one from mom, one from dad.  A genotype is written as 2 letters, each letter represents an allele.

Heterozygous:  has 2 different alleles in the genotype. Ex- Ll

Homozygous: has the same alleles in the genotype Ex- LL or ll

Phenotype: what the dog looks like. Ex- a dog with the genotype ll has the phenotype of a plush coat.

Dominant: an allele that is expressed in the phenotype no matter what other allele you have. Dominant alleles are written as capital letters. Back to our coat length example-  if a dog has the genotype LL or Ll they have a short coat. L is dominant to l, short hair is dominant to long hair.

Recessive: An allele that is only expressed if a dominant allele is NOT present. Recessive alleles are written as lower case letters.  The only genotype a long haired dog can have is ll.  (* Yes, I know there are “smush” coats out there.  There is another gene that modifies coat length aside from “L”).

We all know that you get ½ of your chromosomes from the sire, and half from the dam.  But how can you tell which ones the pups will get? Simple- you can’t. But you can make predictions using a Punnett Square.

Let’s use this sample problem to give you an idea. You breed a heterozygous short haired bitch (let’s say her father was a plush coat so you know she has at least one recessive allele from him) to a plush coated dog. You want to know many plush coated puppies you will get.

Alleles L= smooth coat, l= plush coat

Sire’s genotype- by looking back we remember that he can only be plush coated if he has both recessive alleles, so he must be ll.

Dam’s genotype- as discussed earlier she is heterozygous, so L l. 

Sire gives his offspring either allele

Dam gives either  the L or l allele

The genotypes in the boxes are the possible genotypes of the puppies for this trait…

Ll and ll.  The Ll’s are smooth coated, and 2/4 have this genotype, the other ½ are plush coated like their dad.  Does that mean ½ your litter will be smooth, the other ½ plush?  No.  These genotypes are the possibilities for ONE puppy.  Each puppy has a 50% chance of being smooth coated.  It is like flipping a coin. you have a 50% chance of it turning up heads, but it is possible to flip heads 10 times in a row.  So the puppies could all be smooth coats, or all plush.

 You may be thinking this is too easy to be true- and you’d be right!  Coat color is much more complicated than the simple Punnett square example above.  It is a polygenic trait, which means more than one gene is responsible for coding for the trait of coat color. Not only are there many genes that code for coat color , but there are many unknown genes that modify the genes that code for coat color?  Scientists are still trying to work out the exact inheritance patterns and very few of them agree with each other., I have tried to include as many different theories as possible.

Note- series here refers which series of alleles that the particular gene has, so the Agouti series is the list of alleles for the agouti gene. All alleles are listed in order of dominance, from most to least.  

Remember- your dog has 2 alleles from each one of these series (not to mention a bunch of other ones) controlling their coat color!

Agouti Series : this gene controls the distribution of black hair on the body

Let me give you an example of how this works…in theory Bear (black, with some tan on his legs) and Tessa (dark brown sable) when bred together produced bi-colored pups, dark brown sable pups, and solid black pups.  Solid black is a recessive, so these pups must have the genotype aa… meaning each pup got one of those “a”’s from each parent.. so Bear’s genotype is a ?  and Tessa’s is a ?.   Since Tessa is sable, we know she has the a^w allele, so her genotype is a^wa.  Bear is a little trickier…by looking at his phenotype we know he’s not sable, or black and tan, so he doesn’t carry those alleles. If he was aa the all the puppies he produced with Tessa would be either sable or solid black (try doing the Punnett square!), but that doesn’t explain the bi-colored puppies.  It is my personal guess he is a^ta, and that these two alleles work together (there may be some other modifying genes acting on this as well) to form the darker bi-color.  Does this mean all bi-colored dogs carry the black recessive? It is possible- and it is a pet theory of mine.  If you have a bi-colored dog, or breed one, I’d love to hear from you!

From this Tessa/Bear breeding the bi-colored dogs like Simon do carry the black recessive given to them by Tessa. (If they hadn’t gotten her black recessive allele they would have gotten her sable allele- which is dominant, so they’d be sable!)

There is also an unidentified modification that makes a otherwise solid looking dog have a different colored undercoat.  They are not truly sable (the guard hair are all one color) and don’t carry the sable gene. This appears to be recessive.

B Series – controls the ability of black pigment to form.

http://www.bluedogs.8m.com/liverdec.htm  This site has many pictures of liver colored dogs.

C Series- This gene effects the intensity of pigment produced.  Some believe this is the gene responsible for producing solid white.  White is not a common color in Shiloh shepherds, and it usually only occurs in double MAW litters. 

D Series- Controls the intensity of black pigment.

http://bluedogpics.8m.com/cherokee.htm   This site has some great pictures showing dilute dogs. There can be dilute livers too! 

 E Series- Extension series

Dogs with the ee genotype have the black pigment in their coat fade out by the time they are 2 years old. It doesn’t affect the pigment of the nose or pads. Many people confuse this with a golden sable, the difference is a golden sable dog will have a black tip at the end of its tail an ee dog has a red tip to it’s tail.

Int Series- Controls the intensity of tan markings 

The genes above are the major players in determining coat color in our breed.  There are other ones out there, such as a gene that causes the salt and peppering down the backs of black and tan dogs (thought to be caused by a recessive allele).  There is another series for spotting.

For more information on coat color genetics:

Carver,EA, 1984. Coat Color Genetics of the German Shepherd Dog. J.Hered. 75:247-252

Willis, M.B. 1989.Genetics of the Dog. H.F.&G Witherby, London

Willis, M.B. 1991. The German Shepherd Dog: A Genetic History, H.F.&G Witherby, London

Color Genertics by John Ayotte, Jan 1998 http://www.mindspring.com/~ayottej/frankenhaus/colorgen.htm

German Shepherd Dogs website http://www.cluebus.com/holly/gsdfaq.html#Color

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