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:Nevertheless, the high sequence similarity, overlapping expression domains, and similarities in dimerization partners (Immink et al., 2003) of a number of petunia MADS box genes, especially among members of the same subfamily, suggest that genetic redundancy may be the major cause of the lack of…
Category: