Genetic system of Schwanniomyces alluvius determined by diad analysis of fusion products.

The genetics of Schwanniomyces alluvius, a yeast that secretes alpha-amylase, were investigated. No mating types have been detected in this haploid organism. Hybrids were produced by protoplast fusion, and these were subjected to diad analysis by using two-spored asci. Results showed that the diploidy introduced by cell fusion persists through successive spore generations. It was concluded that in this organism, sporulation is preceded by the fusion of mitotic products, regardless of the ploidy of the latter. Routine procedures for constructing novel strains would, no doubt, be hampered by this failure of the sporulation process to restore haploidy. Nevertheless, chromosomal instability of hybrids, as indicated both by heterogeneity of fusion products and by a high frequency of morbidity among their segregants, may permit the use of classical genetic techniques for strain construction.