On the increase of sites for chromosome exchange formation after chromosome duplication.

Although radiation-induced chromosome exchanges are not distributed among cells according to a Poisson distribution, chromatid interchanges are. In Vicia faba the lack of fit to a Poisson distribution has been attributed to the occurrence of only two sites per cell where the chromosomes are close enough to form exchanges if broken. When chromatid aberrations are induced, after chromosomal duplication, the number of sites more than doubles.