[Theoretical models of chromatid exchange established after endoreplication analysi]

In endoreduplicating cells, two thirds of the chromatid exchanges observed after BrdU treatment are symetrical, like on the two elements of the diplochromosome. The other third seems to occur at random on one or the other element. Each double symetrical exchange would result from a single event occurring at the next to last cell cycle before the mitosis observed. The other exchanges would result from last events of the cycle. Thus the frequency of events would be the same at each cell generation. A theoretical model is proposed which explains the mechanism responsible for chromatid exchanges at the DNA level.