The chromosomes of CHO,an aneuploid Chinese hamster cell line: G-band,C-band,and autoradiographic analyses

Chinese hamster ovary cells (line CHO) have been used extensively for metabolic, genetic, and radiobiological studies with only a superficial appreciation for the degree of aneuploidy characteristic of the line. A thorough karyologic analysis of CHO chromosomes using autoradiographic replication patterns, as well as centromere band (C-band) and Giemsa band (G-band) analysis, is presented. Our results demonstrate that only 8 of the 21 CHO chromosomes are normal when compared with euploid Chinese hamster chromosomes. In the 13 altered chromosomes, we found evidence of translocations, deletions, and pericentric inversions. These altered chromosomes have been characterized with respect to both origin and destination of translocated material. With the exception of the X₂ chromosome, essentially all of the euploid chromatin is present in CHO cells. Autoradiographic replication patterns show that the normal sequence of chromosomal DNA synthesis is altered. Some sites which replicate late in euploid cells replicate early in CHO, and several late-replicating chromosomes in CHO cells replicate in early- or mid-S in euploid material. These studies may serve to elucidate the observed differences in mutagenic behavior between euploid fibroblasts and CHO cells.