HYBRIDIZATION OF YEASTS BY LINDEGREN'S TECHNIQUE

Abstract

An improved version of Lindegren's technique, involving single-cell isolation following mass mating, is shown to be of special value in the breeding of new yeast strains for industrial use and in the mating of “difficult” yeasts. With the introduction of the above modification, Lindegren's technique can be guaranteed to give pure diploid strains and their hybridity can be established with the aid of a sufficient number of genetical markers. For genetical studies on yeast, however, hybridization by Ephrussi's method of pairing haploid cells can be recommended as straightforward and reliable. Tetrad analysis of yeasts has revealed a high frequency of irregular segregation ratios during spore formation suggestive of non-Mendelian inheritance. Various possible explanations for such ratios are considered in some detail and it is shown that, of these, the phenomenon of adaptation, supernumerary divisions in the ascus, plasmagenes and multiple factors probably account for many irregular ratios. On the evidence at present available, the unorthodox theories of Lindegren concerning gene structure and action are considered to be premature.