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:Conditional deletion of CTC1 from mice leads to rapid and catastrophic telomere attrition, early entry into senescence, and signs of telomeric replication defects, such as fragile telomeres and inefficient restart of stalled telomeric replication forks (Gu et al., 2012).
Category: