Mapping the mouse X chromosome: possible symmetry in the location of a family of sequences on the mouse X and Y chromosomes.

Major advances in our knowledge of the genetic organization of the mouse X chromosome have been obtained by the use of interspecific crosses involving Mus spretus-derived strains. This system has been used to study sequences detected by three probes 80Y/B, 302Y/B and 371Y/B isolated from a mouse Y-chromosome library which have been shown to recognize both male-female common and male-female differential sequences. These patterns are due to the presence of a family of cross-reacting sequences on the mouse X and Y chromosomes. Detailed genetic analysis of the localization of the X-chromosome-specific sequences using both a somatic cell hybrid panel and an interspecific mouse cross has revealed the presence of at least three discrete clusters of loci (X-Y)A, (X-Y)B and (X-Y)C. Two of these clusters, (X-Y)B and (X-Y)C, lie distally on the mouse X chromosome, the other cluster (X-Y)A being situated close to the centromere. In situ hybridization shows a striking symmetry in the localization of the major sequences on both the X and Y chromosomes detected by these probes, hybridization being preferentially localized to a subcentromeric and subtelomeric region on each chromosome. This striking localization symmetry between the X and Y chromosome sequences is discussed in terms of the extensive pairing of the X-Y chromosomes noted during meiosis.