
Ok, in my breed it has been known for a stub/full tail mating to produce an all tailed litter, however, offspring from that in a tail/tail mating have produced a stub, although a longer stub.
Different breed, but so far as vallhunds are concerned both in the UK and Sweden they have never managed completely to discover exactly what genetic factors there. Roughly however
Tail/tail - will produce all tails most of the time, very occasionally you will get a longer stub.
Tail/stub - mixed litter
Stub/stub - mixed litter - though litter size is on average smaller - possibly due to a lethal tail gene causing reabsorbtion - this however is not proven.
Stub/stub matings are not recommended.
we have every tail length within the gene pool, from a full length tail, via longer stubs, proper bob tails and even inverted tails where the end vertebrae are missing completely.