In the first 2 activities, students working in small groups receive a series of model viruses. These include each of several types of nucleic acid genomes (DNA/RNA, ds/ss, +/- strands). In one set of activities, students sequentially examine the variety of modes by which the genomes are replicated and the dependence of mechanism upon the form of nucleic acid. In a second series of activities, small groups examine the steps in the normal flow of information from cellular genes to mRNA. Students then examine viral genomes of different compositions and identify how the message is made once the genome has entered the host cell. In the third activity, students are given a hypothetical protein, then they are directed to back-translate from the amino acid sequence to the original viral nucleic acid sequence found in that specific virus.