Preferential occurrence of sister chromatid exchanges at heterochromatin-euchromatin junctions in the wallaby and hamster chromosomes

Chromosomes of two mammalian species, the white-throated wallaby and the rat-like hamster, possessed large amounts of constitutive heterochromatin which is detectable as C bands. By making use of this character, the frequency of sister chromatid exchanges (SCEs) was determined for the C band and the euchromatic regions of the chromosome. In both species, the distribution of SCEs in the euchromatin of chromosomes was found to be proportional to its metaphase length, while the number of SCEs localized in the C band regions was clearly fewer than expected on the basis of the relative length of those regions at metaphase. Many SCEs were, however, detected at the junctions between the euchromatin and the C band heterochromatin. All of these findings were consistent with previous observations on the Indian muntjac and the kangaroo rat chromosomes.