MUTATIONAL DISRUPTION OF THE 9 + 2 STRUCTURE OF THE AXONEME OF

A mutant of Chlamydomonas, gant-5, which has short but variable-length, paralysed flagella has been characterized using electron microscopy and genetics. The flagellar axoneme shows varying degrees of disorganization of its 9 + 2 structure, and the structures that attach to the microtubule pairs may be wholly or partly missing or, if present, abnormal. Flagellar length is inversely related to temperature, and gametes of this mutant are generally incapable of mating at higher tem-peratures. This pleiotropic mutation shows Mendelian (2:2) segregation and is unlinked to the mating-type locus. It is suggested thatgam-5 leads to the production of a thermal-sensitive flagellar component, which results in increased assembly and/or maintenance difficulties as temperature is increased