Fig. 1.

The lambda decision circuit measures the MOI even as the viral copy number is changing. A higher MOI increases the propensity to lysogenize. Here, infection by a single lambda phage (Top) results in lysis, whereas coinfection by two phages (Bottom) leads to lysogeny. In choosing cell fate, the infecting phage must respond to the initial number of viral genomes in the cell but ignore the subsequent increase in number because of viral replication.