Telomerase activity in HMEC decreases with age. (A) TRAP gels for 34 strains of 4th passage pre-stasis HMEC. Histograms showing distributions, with their associated means, of (B) age, (C) RTL, (D) PD at stasis, (E) percentage LEP of total, (F) percentage MEP of total, and (G) percentage cKit + of total, in HMEC strains. Strains with TRAP activity are represented on the white histograms, and strains with no detectable activity are shown on the black histograms. Strain 173T, which are HMEC that originated from within a dissected breast tumour, was excluded from the analyses.