DISTRIBUTION OF SISTER-CHROMATID EXCHANGES IN DIFFERENT TYPES OF CHROMATIN IN THE X-CHROMOSOME OF MICROTUS-CABRERAE

We used the X chromosomes of Microtus cabrerae as a model to analyze t he distribution of sister chromatid exchanges (SCEs) on different type s of chromatin, because of the marked heterogeneity of the heterochrom atin in the entire short arm and a portion of the long arm of this chr omosome. Computer-simulated distributions, according to an algorithm t hat makes it possible to modify the distribution on the basis of any p ossible hypothesis, were compared with real distributions by log-linea r models. We found that the frequency of SCEs in different types of he terochromatin was higher than that expected for a random distribution, and located an SCE hot-spot at the junction between euchromatin and h eterochromatin. The possible relationship between the distribution of SCEs and base composition or chromatin accessibility are discussed.