[Linear differentiation of the X-chromosomes of the field vole Microtus agrestis]

Morphology of the fibroblasts X-chromosomes obtained from the female field vole Microtus agrestis and cultured for 4--5 hr before fixation in 5-bromodeoxyuridine, was studied. A clear differential condensation along the lenght of the whole X-chromosome was observed. A difference between homologues in the degree of uneven condensation was noted both in the short arm (facultative heterochromatin) and in the long arm (constitutive heterochromatin).