Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:pclk-1::clk-1 ∆MTS (13-187)::gfp was generated by mutagenesis of the pclk-1::clk-1::gfp plasmid.
Category: