Heterogeneous heterochromatin and size variation in the sex chromosomes of Microtus cabrerae.

The sex chromosomes of Microtus cabrerae are characterized by large segments of constitutive heterochromatin in both the X and Y. Alkali treatment, enzymatic digestion (trypsin), and fluorochrome staining reveal considerable heterogeneity within these heterochromatic blocks and allow us to distinguish several regions. In addition, variation in the length of these segments is also present, probably as a result of deletions. A possible explanation for the origin of these heterochromatic blocks is discussed.