Fig. 3. (A) Elevated telomere sister chromatid exchanges (T-SCEs) in G5 mTerc^–/– Wrn^–/– cells. Unequal T-SCE generates one sister chromatid with long telomere lengths at the expense of the other. The resulting daughter cell inheriting the shorter telomeres will undergo replicative senescence, whereas the daughter cell with longer telomeres will have increased proliferative capacity, perhaps able to maintain telomere lengths indefinitely through this ALT mechanism.