Segregation studies in CHO hybrid cells: I. Spontaneous and mutagen-induced segregation events of two recessive drug-resistant loci.

The process of segreation or phenotypic expression of two recessive drug-resistant loci from heterozygous Chinese hamster ovary hybrid lines is examined. The spontaneous segregation rates of phytohaemagglutinin resistance (Phar) and a temperature-dependent 8-azaguanine-resistant locus (Azarts) from heterozygous quasitetraploid lines using Luria-Delbruck fluctuation analysis were 5 X 10(-5) and 10(-5) events/cell/generation, respectively. In quasihexaploid lines, the latter rates increased 40- and 200-fold, respectively, and were dependent on the number of presumptive drug-sensitive allelel. The mutagens EMS, MNNG, ICR-170, ICR-191, and gamma rays significantly increased the frequency of segregation events. The mutagen-induced frequency of dominant mutations to ouabain (Ouar) and alpha-amanitin (Amar) rsistance in the same hybrid line was much lower in comparison to segregation events and was mutagen specific. The chromosome number per metaphase cell was more variable than DNA content in quasitetraploid lines. These properties of marker segregation are consistent with mechanisms of either restricted chromosome loss, rearrangement, or mutation.