Explain how a trait might seem to “disappear” for a generation, and then “reappear” in the following generation.

This state is characteristic for recessive traits. For an individual to express a recessive trait, it must have two recessive alleles (one of two or more alternative forms of a gene) of the responsible gene. But, if it has one recessive allele and one dominant allele, it will not have the trait, but he will be called a carrier. So, it seems like the trait "disappeared" but still it is "carried" in the genome. However, if its offspring has two recessive alleles and express the trait, it will seem like the trait "reappeared".