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:Polymorphism on Chr Y was detected by polymerase chain reaction (PCR) for zinc finger protein 2, Y linked (Zfy2) with primer pairs (forward primer 50-GTGAGAGG CACAAGTTGGC-30 and reverse primer 50-GTGCTCCTG GTATGGTGTAT-30) for distinguishing Chr Y between Mus musculus musculus and Mus musculus domesticus (Prager et al. 1997).
Category: