In cocker spaniels, solid coat color is dominant over spotted coat color. If two heterozygous dogs were crossed to each other, what would be the probability of having a first litter of 6 pups, the firstborn with spotted fur, and then among the next 5, 4 with spotted fur and the rest with solid fur; and then a second litter of 7 pups, 1 with spotted fur and the rest with solid fur?

Let's say that solid coat is expressed with S and spotted coat color is expressed with s. This means that the two heterozygous cocker spaniels have Ss as their genomes. This results in the probability of 75% solid coat (SS and Ss) and 25% spotted coat (ss) in the offspring.

The probability of the firstborn pup in the first litter having spotted fur would be 25%. The probability of 4 out of the 5 remaining pups having spotted fur is 1/4 x 1/4 x 1/4 x 1/4 which is 1/256.

The probability of the second litter having 1 pup with spotted fur is 25% and the 6 remaining pups with solid fur can be calculated as above by multiplying 3/4 6 times which is 64/4096 or 1.5%.

I hope this answer helps.