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:an XX/XY or ZZ/ZW system, respectively), individuals of the heterogametic sex possess sexspecific genomic regions for which sex-specific molecular genetic markers can be developed (Gamble 2016; Griffiths and Tiwari 1993).
Category: