Normal Distribution of Cell Generation Rates

Abstract

THE distributions of generation time are markedly skewed, but the reciprocal of the generation time, termed ‘generation rate’, was reported to have a normal distribution for a bacterium, yeast, a strain of human tissue culture, and the protozoan Tetrahymena geleii; these results provided evidence for the generalized nature of this distribution in widely different kinds of cells in balanced growth¹. Although other measurements had not always given a normal distribution of generation rates, this was to be expected since the sources of experimental bias were not then completely understood. There are several kinds of bias that must be avoided². Furthermore, some experiments in the literature have given no clear test of the nature of the distribution, since data are insufficient, with rather fewer than 100 cell divisions measured. Nevertheless, it has been asserted that the skewed character of the generation-time distribution has decreased as experimental techniques have advanced³, and this would require that the generation rates depart from a normal distribution. This communication presents further evidence for the validity of the normal distribution for generation rates.