Dominance is a rather old-fashioned term not much used by working geneticists anymore which describes a situation in which a gene is expressed when in a single dose. What this means is you can see the effect of the gene if the pup in question only had one parent with the trait. (And it means the pup HAD to have one parent with the trait, but could have had two). There are not a lot of examples of clear dominance & even fewer examples of undesirable traits that are clearly & simply dominant, because you simply do not breed the dog who has it and it is gone. Ticking is a typical example. You don't want ticking then don't breed, for example, to a dog who has it or at least half your pups from a clean white momma with be ticked. Nice part of simple dominance is, if you don't see it you don't have it. Of course, most 'dominant' genes are incomplete dominants, or dominants with variable expression or incomplete penetrance. Incomplete
dominance means two genes will "war" over which gets expressed and you can likely see a bit of each in the dog. A simple example is white piebald spotting; the dominant gene for self-(full)-coat color cannot cover the dog in pigment when it is not in two doses, so hybrid pups get some white markings (beyond just chest and toes) & two such "hybrids" bred together can produce white pups. Incomplete dominants give you a range & you cannot really control the exact spread of their effects. Variable expression is like incomplete dominance with the gene acting all alone: it is erratic in what it will do. Incomplete penetrance is a population comment. It means that only a certain percentage of the population that HAS the gene will show the effect of the gene. You got it, but only got an 80% chance of ever seeing its effects. In all these cases, for breeders, these are hard to control, and any example of expression must be taken for proof the gene in in the line-to act cautiously & responsiblity-and pedigrees should be so marked. These sorts of complex dominance problems cannot be treated as simple dominance is. The "responsible" party may be hard to identify.