Evaluation of apoptosis in unicellular, unilineage erythroid cultures. Single cells were scored apoptotic if no cell division(s) was detectable or if no cell(s) was detectable after 10 days of culture. At inititation of single-cell culture, each well was monitored by an inverted microscope. Only wells containing 1 cell were monitored. The proportion of single apoptotic cells was evaluated for freshly sorted CD34⁺CD38⁻ cells or purified CD34⁺Lin⁻ cells (A), siblings thereof, ie, after the first cell division (B), and single cells after 2 cell divisions (C).