IN-SITU ANALYSIS OF CENTROMERE SEGREGATION IN C57BL 6 X MUS-SPRETUS INTERSPECIFIC BACKCROSSES/

The analysis of major satellite sequence differences between Mus spret us and laboratory mice provides a robust method for analyzing the cent romere location for the genetic maps of each mouse chromosome. Fluores cence in situ hybridization (FISH) of a genomic probe, pMR196, for the laboratory mouse major satellite sequences was used to identify C57BL /6Ros (B6) pericentromeric heterochromatin in progeny of reciprocal ba ckcross matings. These included 80 (B6 x M. spretus)F1 x M. spretus pr ogeny (BSS) and 70 (B6 x M. spretus)F1 x B6 (BSB) progeny. FISH analys is of pericentromeric heterochromatin was conducted on the same metaph ase spreads that were karyotypically analyzed for chromosome-specific banding patterns. Analysis of chromosomal segregation suggested that t here was not primary deviation from random assortment during meiosis i n the interspecific hybrid female, because nearly all of the 190 pair- wise comparisons did not deviate from expected and because there was n o consistent pattern of deviation of the same chromosomes in the recip rocal backcross progeny from similar (C57BL/6 x M. spretus)F1 hybrid f emales. These results affirm the value of using the major satellite to genetically mark pericentromeric heterochromatin in the analysis of t he segregation and assortment of centromeres in Mus interspecific cros ses.