Printed in Great Britain KARYOTYPIC ANALYSES OF PARENTAL AND HYBRID INTRASPECIFIC MOUSE CELLS, A9/B82, BY GIEMSA- AND CENTROMERIC- BANDING

Hybrids between Ag (HGPRT-) and B82 (TK-), mouse heteroploid fibroblast lines, were obtained through continuous cultivation and clonal selection; such hybrids showed marked segregation and by conventional stains displayed chromosome numbers and distribution similar to that of either parental type. Detailed analyses by Giemsa (G)- and centromeric-banding of these parental lines, and of 4 of the reduced hybrids, maintained in culture for up to 5 years, revealed the following points: (1) The distribution of the majority of individual chromosomal classes was similar for 3 of the hybrid cell lines. (2) Over two-thirds of the chromosomal arms in both the parental lines and hybrid lines were identical to normal mouse telocentric chromosomes. (3) For 2 of the hybrid lines, segregation was particularly marked with respect to those chromosomal arms whose G-banding patterns were identical to the wild-type genome; this indicated that segregation had occurred at the expense of redundant chromosomal material introduced by cell fusion. These banded studies demonstrated that segregation chiefly accounted for the sharp reduc-tion in chromosome numbers while recombination accounted for the chromosome hetero-geneity of the hybrid cells as compared to the parental genomes