MODELING THE KINETICS OF CHROMOSOME EXCHANGE FORMATION IN HUMAN-CELLSEXPOSED TO IONIZING-RADIATION

A biophysical model has been applied to study the kinetics of chromoso me exchange formation in human cells. Chromosomal exchange induction ( for example dicentrics) by ionising radiation was modelled by means of the Monte Carlo technique. This involved energy deposition by electro ns, production of chromosomal breaks (assumed to be DNA double-strand breaks) and their repair and exchange. Exchanges were assumed to resul t from pairwise interaction between two DNA breaks in a distance-depen dent manner. The rate at which exchanges are formed was found to depen d upon how the exchange to no-exchange probability ratio varied with t ime. The assumption that this ratio did not alter with time produced a time constant for the formation of exchanges which was exactly half t hat of the repair time constant. Longer time constants could not be ac commodated unless the probability ratio for exchange increases with ti me, Different time constants for inter- and intratrack exchanges could be achieved on the basis of DNA double-strand break separation.