Figure 8. DNA synthesis in age-synchronized cultures.

A. Baby machine. Mother cells (dark blue) are immobilized to the underside of a membrane through which media flows. Newborn cells (pale blue) are shed into the effluent. B. Age distribution of mothers. For exponentially-growing cells, newborn cells are twice as likely as those about to divide. C. In the effluent, the age distribution is inverted in time – first daughters from old mothers, then daughters from young mothers. D. DNA synthesis rate in the mothers. A step increase in DNA synthesis rate, corresponding to initiation of a round of DNA replication, occurs at an age a_i. E. As in panel B, the step-increase in DNA synthesis rate (measured using radioactive nucleotides) is inverted in the daughters, and occurs a time a_i before the division event. Panels B–E redrawn from [148].