Genetic Question - Page 1

In German Shepherds, you have 4 main color pattern genes.  Sable, Black & Tan, Bi-color, and Black.  These are listed in order of dominance, with Sable being the most dominant gene and Black being the most recessive.  Modeling GSD coat patterns as simple mendelian genes has, thus far, proved successful, so thats the model thats generally used. 

Every dog has 2 coat color/pattern genes.  They get 1 from mom and 1 from dad.  Of the 2, the more dominant trait is the one that is expressed.  So for example, lets say that a puppy was given a sable gene by mom and a bi-color gene by dad.  The puppy would turn out Sable because thats the more dominant trait.  Even though the puppy is Sable, he will still carry BOTH genes and have the potential of passing each gene to his offspring.  The 2 genes together (the sable and the bi-color) is called the "genotype" and the physical characteristic thats produced in the dog (the Sable coat color) is called the "phenotype".

There are 2 different genotypes that can cause an offspring to be bi-color, due to its place in the heirarchy of dominance:  bi-color and bi-color (called homozygous) or bi-color and black (called heterozygous).  These are the only 2 possible combinations because if the offspring is given a black & tan gene or a sable gene by one of the parents, then those genes, being more dominant, will override the bi-color and the offspring will express the more dominant trait. 

So, you're really asking the wrong question here.  The question should not be one of the color of the parents... because theoretically, 2 sable dogs being bred together can produce a bi-color puppy so long as each sable parents recessive trait is bi-color or one has a bi-color recessive and the other has a black recessive.  In that hypothetical, the chances of a puppy receiving both recessive traits from the breeding is 25%. 

Remember, when you are looking for a specific coat color/pattern, you have to consider the recessive, non-expressed, gene that the parent possesses just as you do with the dominant gene.  Just because the dominant traits is expressed, doesnt mean that it increases the odds of it being passed on over the recessive trait.  Figuring out what the recessive gene is can be difficult at times because, obviously, its not being expressed. 



 

P.S. - If you want a greater understanding of how genes are inherited and how pedigrees are assessed, then a great book to read would be Control of Canine Genetic Diseases by Dr. George A. Padgett, DVM.  While the book is centered around genetic diseases and how breeders can find, isolate, and avoid them, the book also goes into the different modes of inheritance and is an all around good book for anyone who is interested in understanding canine genetics.  He does a good job of making it easy to read and understand.  It was written for the average breeder, trainer, dog lover who is NOT a PhD in genetics.  I highly recommend it. 

Glad I could help.

Keep in mind if you were to say want to produce bi-color puppies with your dog that you stated had 2 sable parents, you cannot assume that if you breed it with a bi-color or bi-color carrier that the puppies will have a chance to come out bi-color. If your dog inherited Sable color gene from both parents because both obviously express it therefor he/she could very well have inherited sable from both then the dominant sable homozygous  set up in your dog would make it that 100% of all his/her puppies will always come out Sable regardless of the dog you breed it to as if a puppy has even one Sable gene it will be expressed, since in this situation all the genes they get from your dog in this senario would be Sable all puppies would always be Sable.