Dominance has nothing to do with which genes are expressed. It's not about one allele "recognizing" and shutting off the other. Generally speaking for a gene on an autosomal chromosome, both alleles will be expressed. Dominance is a question of whether the effect of one allele can mask the effect of another. So for example let's say you had an allele that produces a protein which is toxic in some way and thereby causes a disease. Then even in a heterozygous organism the single copy of this toxic allele might be enough to produce the diseased phenotype and therefore that allele would be classified as dominant. The healthy version of the protein would still be present in cells but that doesn't matter. I recommend you read the "molecular mechanism" section on the wikipedia article on dominance for more examples and details.