CHARACTERIZATION OF A SMALL FAMILY (CAIII) OF MICROSATELLITE-CONTAINING SEQUENCES WITH X-Y HOMOLOGY

Four X-linked loci showing homology with a previously described Y-link ed polymorphic locus (DYS413) were identified and characterized. By fl uorescent in situ hybridization (FISH), somatic cell hybrids, and YAC screening, the X-linked members of this small family of sequences (CAI II) all map in Xp22, while the Y members map in Yq11. These loci contr ibute to the overall similarity of the two genomic regions. All of the CAIII loci contain an internal microsatellite of the (CA)(n) type. Th e microsatellites display extensive length polymorphism in two of the X-linked members as well as in the Y members. In addition, common sequ ence variants are found in the portions flanking the microsatellites i n two of the X-linked members. Our results indicate that, during the e volution of this family, length variation on the Y chromosome was accu mulated at a rate not slower than that on the X chromosome. Finally, t hese sequences represent a model system with which to analyze human po pulations for similar X- and Y-linked polymorphisms.