Figure 2.

Loose and stringent transmission bottlenecks. Transmission of influenza (dashed vertical line) reduces the observed diversity of the virus population in the recipient host. (A) Stringent transmission bottlenecks significantly reduce the diversity observed in the recipient host by transmitting only a few virus particles, making them prone to stochastic fluctuations in variant frequency. (B) Loose transmission bottlenecks transmit a higher diversity of virus particles, allowing selection to act on the virus population in the recipient. In both cases, genetic diversity will increase as the de novo variants are generated through the replication of influenza.