What is the only way that a recessive trait will show up in offspring?

The only time a recessive trait will be passed on to the offspring is if both the parents have the recessive genotype. For example, if the parents had the genotype Bb x Bb, there were be a 25% chance of a recessive genotype in the offspring. If both the parents are recessive, there is a 100% chance that the offspring will be recessive.