CHROMOSOME-DESIGNATED MUTATION SELECTION IN TETRAHYMENA THERMOPHILA

M. I. Altschuler ¹ and P. J. Bruns ²

¹ Section of Genetics, Cornell University, Ithaca, New York 14853
² Section of Development, Cornell University, Ithaca, New York 14853

Two protocols are presented that allow the selection of mutations mapping to micronuclear chromosome 5 in Tetrahymena thermophilia . One protocol involves crossing mutagenized diploid cells directly to a strain nullisomic for chromosome 5 and screening the monosomic progeny for a mutant phenotype. The second protocol first takes the mutagenized diploid cells through round I of genomic exclusion to create useful and reusable mutant heterokaryons, which are then assayed for the presence of mutations on chromosome 5 by crossing to the nullisomic 5 strain. Of 14 putative chromosome 5 mutations obtained by these two methods, seven are shown by genetic analysis to be recessive mutations on chromosome 5; one mapped elsewhere in the genome; six were infertile or failed to yield progeny in some of the diagnostic crosses and, thus, their genetic nature could not be determined with certainty.