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:Conditional double mutants of trf4 with top1-7 showed ribosomal DNA (rDNA) condensation phenotypes (Sadoff et al, 1995; Castano et al, 1996), and were reported to display defects in mitotic segregation (Wang et al, 2000; Edwards et al, 2003).
Category: