Paternal versus Maternal Inactivation in the X Chromosome of Female Mice

Abstract

EVANS et al.¹ have shown that a “late labelling” X chromosome occurs in normal somatic cells of the mouse. Using female mice, heterozygous for the Cattanach translocation, in which an autosomal segment is inserted into an X chromosome making the translocated chromosome (X^t) recognizable as the longest member of the complement², they showed that this abnormally long chromosome was “hot” in about half the cells that contained a late-labelling chromosome. In the remaining cells, the hot chromosome was always one of the long chromosomes and was presumed to be the Xⁿ chromosome. These observations were interpreted as supporting evidence for the postulate of random inactivation³ of the maternal and paternal X chromosomes.