The following is to help understand how the blue gene is passed. I have seen a blue carrier bred to a blue dog produce an all-blue litter and it is possible for a blue carrier to a blue dog to have a litter of all blue carriers (but no blue puppies). Mother Nature doesn't always do things consistently. But it helps to understand the basic genetics of it. I did find a web site that further explains gene inheritance - here is a link:
http://anthro.palomar.edu/mendel/mendel_2.htm
What to expect in blue litters:
If a blue dog (d/d, with two copies of the recessive "blue gene") is bred to another blue (d/d), all of the resulting puppies will also be blue
(d/d).
If a blue dog (d/d) is bred to a carrier of the blue gene (D/d), ALL of the puppies will be carriers of the blue gene (D/d), and 1/2 of the puppies
will be blue (d/d).
If a blue dog (d/d) is bred to a non-blue who is NOT a carrier of the blue gene (D/D), ALL of the puppies will be carriers of, but will not express, the blue gene (D/d).
If a carrier of the blue gene (D/d), is bred to a non-carrier (D/D), 1/2 of the puppies will be normal non-carriers (D/D) and 1/2 will be carriers (D/d).
If two carriers are bred together (D/d x D/d), 1/4 of the puppies will be blue (d/d), 1/2 will be carriers (D/d), and 1/4 will be normal non-carriers (D/D).
Some people mistakenly believe that even though a dog may have a blue dog in its ancestry, that if no blues have been produced in several generations that means that their dog can't be carrying the blue gene. This is wrong. It is not like mixing paint in a bucket, progressively diluting out the gene. A recessive gene will keep passing hidden and unchanged through an infinite number of generations of carriers. The thing about a recessive gene is that carriers pass the gene on to about 1/2 of their offspring, producing another generation of carriers; then those carriers pass it on to 1/2 of their offspring, and so forth, so that the gene spreads unnoticed through the gene pool as people unaware of an carrier ancestor breed its descendents. It will only surface when a carrier is bred to another carrier (or to a blue).
