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:Instead of using the single fuzzless locus mutant developed mapping populations (Rong et al. 2005, 2007; Zhang et al. 2005; Guo et al. 2006; Wan et al. 2007), the common female parent line of the two F2 populations we developed combined at least two fuzzless loci (N1 and n2, and probably n3)…
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