multi-generation stub tail + stub tail breeding is in reality no different
from one generation. there is no accumulative effect associated
with the t-box mutation. stub tailed dogs only have one dose of the
gene (heterozygous) irrespective of their parents, or grand-parents.
nothing can change. there is no significant science to show that
multigeneration breeding of only stub tails + stub tail dogs creates
any negative outcomes for puppies. neither can multigeneration
breeding of stub tail + stub tail pairings alter ratios of stub tail / tailed puppies in the litter.