Fig. 2. Metaphase singlets in pre-senescent cells aged in vivo. Fibroblasts derived from three elderly people (y, years) were propagated in culture from cell line establishment until senescence. Pre-senescent cells (PD 15-30) were subjected to combined FISH-IF at 1-2 PDs before senescence, using probes for the telomeric and control regions indicated. The mean percentage (±s.d.) of chromosomes displaying a singlet signal is indicated, together with the P value of the binomial distribution probability analysis (^*P<0.0001). The number of chromosomes scored for each probe is indicated in the bar.