Karyotypes of Saccharomyces sensu lato species

An improved pulsed-field electrophoresis program was developed to study dif ferently sized chromosomes within the genus Saccharomyces. The number of ch romosomes in the type strains was shown to be nine in Saccharomyces castell ii and Saccharomyces dairenensis, 12 in Saccharomyces servazzii and Sacchar omyces unisporus, 16 in Saccharomyces exiguus and seven in Saccharomyces kl uyveri. The sizes of individual chromosomes were resolved and the approxima te genome sizes were determined by the addition of individual chromosomes o f the karyotypes. Apparently. the genome of S. exiguus, which is the only S accharomyces sensu late yeast to contain small chromosomes, is larger than that of Saccharomyces cerevisiae. On the other hand, other species exhibite d genome sizes that were 10-25% smaller than that of S. cerevisiae. Well-de fined karyotypes represent the basis for future genome mapping and sequenci ng projects, as well as studies of the origin of the modern genomes.