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:Cohorts of tg mice expressing mutated G37R-hSOD1 were bred and identified by genotyping of tail DNA as described (Martin et al., 2007, 2009; Wong and Martin, 2010).
Category: