Coat pattern question: What controls a pup being bi?

[Bacon_Army]

Hello. I'm getting a pup in the fall, and I just want to know what the possible coat patterns for the litter are.

The Dam is a black and tan ('blanket back' I think it's called). Her dam is a solid black, and her sire is black and tan. The Sire is a bi-colour. His dam was a solid black and his sire was a bi-colour.

I know that some blacks are possible in the litter (as both have the recessive black allele, probably 4:1), but what controls if a pup will appear bi, or black and tan? I'm trying to make a punnett square, but I don't know which is dominant, or if there are a combination of other factors that determine the appearance of the bi pattern!

In the end, the personality of the pup is all that will matter, but I'm just curious as to what the odds of a bi-colour would be.

[GsdLoverr729]

Another member made this chart on color genetics:

http://www.ehretgsd.com/GSDcolorGenes.pdf