The over-dispersion between cells of chromosomal aberrations

A survey of the literature suggests that random dispersion of radiation induced aberrations occurs only when uniform fields of predominantly low LET radiations act on cell populations which are homogeneous with regard to cell type, cycle stage and intrinsic radiosensitivity. The in vitro irradiation of unstimulated human lymphocytes with X- or γ-rays is an example of this. Over-dispersion is observed in all other cases where sufficient data have been obtained and where there are a sufficient number of chromosomes per cell to prevent underdispersion through distortion.The observation is made that the sum of two or more Poisson populations with different means gives an over-dispersed population. This is used to make a unified explanation of the various observations of overdispersion of aberrations between cells.