An example method includes reacting a first solution and a different, second solution on a flow cell by flowing the first solution over amplification sites on the flow cell and subsequently flowing the second solution over the amplification sites. The first solution includes target nucleic acids and a first reagent mixture that comprises nucleoside triphosphates and replication enzymes. The target nucleic acids in the first solution transport to and bind to the amplification sites at a transport rate. The first reagent mixture amplifies the target nucleic acids that are bound to the amplification sites to produce clonal populations of amplicons originating from corresponding target nucleic acids. The amplicons are produced at an amplification rate that exceeds the transport rate. The second solution includes a second reagent mixture and lacks the target nucleic acids. The second solution is to increase a number of the amplicons at the amplification sites.