Random segregation of multiple genetic markers from CHO-CHO hybrids: Evidence for random distribution of functional hemizygosity in the genome

The linkage relationship between various recessive markers isolated in Chinese hamster ovary (CHO) cells has been investigated. For such studies, multiple recessive markers conferring resistance to various drugs, e.g., resistance to emetine (Emtr), thioguanine (Thgr), azaadenine (Azar), phytohemagglutinin (Phar), diphtheria toxin (Dipr), toyocamycin Toyr), aminopterin (Amnr), and methylglyoxalbisguanyl hydrazone (Mbgr), were introduced into CHO lines by selecting successively for one drug at a time. Hybrids were constructed between the multiply marked lines and the sensitive cells, and segregation frequencies for the various markers, singly and in different pairs, were examined. Results of such studies show that of the recessive markers examined, none cosegregated from the hybrid cells. The independent segregation of the X-chromosome-linked Thgr and of the rest of the markers indicates that none of these other mutations are located on the X chromosome. These results also provide strong suggestive evidence that functional hemizygosity in CHO cells is not restricted to one or a few chromosomal regions, but rather appears to be widespread.