On correcting the error due to metaphase degeneration in stathmokinetic studies

Metaphases arrested by stathmokinetic agents have a limited life span. This may have to be taken into account in drawing conclusions from experiments whose duration is of the same order as the average metaphase life span, or, in the case of a combined arrest and labelling experiment, if G2 is of long duration. The average life span of arrested metaphases in the tissue under study can be estimated by a simple experiment which isolates the G2 cohort. This enables the investigator to decide whether he can trust his metaphase count without correction for loss due to degeneration. If the proposed experiment requires an accumulation of arrested metaphases over a period longer than the average life span of an arrested metaphase there is a serious risk of under-estimating the metaphase index. We propose a simple method of assessing the magnitude of this risk, and making the necessary correction. Assuming that metaphase degeneration is a random process a corrected index of arrested metaphases can be found for expanding populations multiplying the observed metaphase arrest index by exp (λ-β) (t-m)], where m is the minimum life span of an arrested metaphase, t is the time point from the onset of the experiment, and β and λ are rates at which metaphases are formed and degenerate, respectively. A slight modification of this formula adapts it to steady state systems.