EVOLUTION OF A LONG-RANGE REPEAT FAMILY IN CHROMOSOME-1 OF THE GENUS MUS

Copy numbers and variation of a clustered long-range repeat family on Chromosome (Chr) 1 have been studied in different species of the genus Mus. The repeat sequence was present in all, as inferred from cross-h ybridization with probes derived from the Mus musculus repeat family. Copy numbers determined by dot blot hybridization were very low, from three to six per haploid genome in M. caroli, M. cervicolor, and M. co okii. These species form one branch of the phylogenetic tree in the ge nus Mus. In the other group of phylogenetically related species-M. spi cilegus, M. spretus, M. musculus and M. macedonicus-copy numbers range d from 6 to 1810 per haploid genome. The repeat cluster is cytogenetic ally visible as a fine C-band in M. macedonicus and as a C-band positi ve homogeneously staining region (HSR) in several populations of M. m. domesticus and M. m. musculus. When cytogenetically visible, the clus ters contained from 179 to 1810 repeats. Intragenomic restriction frag ment length polymorphisms (RFLPs), which reflect sequence variation am ong different copies of the long-range repeat family, increased with h igher copy numbers. The high similarity of the RFLP pattern among geno mes with C-band positive regions in Chr 1 of M. m. musculus, M. m. dom esticus, and M. macedonicus points to a close evolutionary relationshi p of their Chr 1 repeat families.