Tetraploid Saccharomyces

Abstract

SUMMARY: A yeast hybrid heterozygous for many alleles produces an occasional ascus in which instead of the expected 2 dominant:2 recessive segregations one finds 4 dominant:O recessive ratios for most of the characters. The single ascospore cultures are often incapable of copulating with either mating type. Genetical analysis has revealed that such asci contain ascospores which are diploid and heterozygous for the mating type alleles and other characters. The single ascospore cultures, heterozygous for mating type, may sporulate and by characterization of their progeny the genotype of the ascospore can be determined. Other diploid cultures originating from single ascospores are homozygous for mating type. Cells from these cultures (unlike the diploid cells heterozygous for mating type) are capable of mating, and when mated with similar cells of complementary mating type produced tetraploid yeasts. Triploids were produced by mating diploids with haploids. The tetraploid segregates to produce the expected tetrad types and gametic ratios. Some sporulating cultures produced unexpected types of asci for characters controlling sugar fermentation but interpretation of their significance is not feasible since our customary control of breeding procedure does not apply in the analysis of diploid cultures which sporulate on ordinary agar slants. METHODSSafeguards in the breeding procedure. We have developed a breeding procedure which excludes errors due to intervening sporulations and copulations between the generations which are analysed. In the earlier phases of this work single ascospore cultures which produced spores were not unusual (Lindegren & Lindegren, 1944). A rigid programme of selection was established and sporulating haplophase cultures were never used as parent breeding stocks. Diplophase cultures were never maintained as sources for breeding stocks since sporulation would be expected to occur and would quickly render them heterogeneous. Non-sporulating single ascospore haploid cultures were preferred as breeding stocks, since a minimum of variation occurs when they are carried on a rich nutrient medium by heavy transfers. A mating is made by mixing two heavy inocula of these cultures in a small amount of broth and transferring the cells to presporulation agar as soon as zygotes appear. On the presporulation agar, growth of both haplophase and diplophase occurs but spores are not produced. Most of the cells from the presporulation agar are transferred to gypsum. The immediate descendants of the zygotes sporulate while the haplophases do not. Each haploid culture used in a mating is carefully tested for its ability to sporulate by growth on presporulation agar followed by transfer to gypsum. Those which show any tendency to sporulate under these conditions are not used.The advantages of our procedure are as follows: (1) Non-sporulating strains (haplophases) constitute the breeding stocks. (2) The composition of the

A Thiamine-Requiring Mutant of The Tomato

“…The only effective treatment was the vitamin mixture, which produced a pronounced greening of the tissue after _ 2 days and a complete disappearance of the deficiency symptoms after 5 days of application. The active vitamin of the mixture was shown to be thiamine by means of the screening test described by Lindegren and Lindegren (1951). After mutant plants, which received three treatments with thiamine (2 mg per 100 ml water) per week, had been grown for about four months, they were almost indistinguishable from the wild-type.…”

THE ISOLATION AND IDENTIFICATION OF POLYPLOID STRAINS OF USTILAGO VIOLACEA

“…the r It is interesting to compare these results with those for polyploids in other fungr. ln A. niduli.ns (Roper, 1952;Ponte coryo et al, 1954) and in some strains of Saccharomyces trrritttoi llindegren and Lindegren, 1951;Gunge and Nakatomi, 1972) t'he mean cell volume,/single genome remains approximately constant' The large irrcreare in cell volumes wiih increasing ploidy reported in this paper for stationary phase cells of Ustitago viol'acea seems to be unique' Mundkur (1953) analysed interphase nuclear size in saccharomyces and showed that the nuclear volume in haploid, diploid, triploid and tetraploid:!t"Tt increased in the ratio ! : 4 : 9 : t4.-These ratios are almost identical with the uuto", reported here for U. violacea.…”

“…Only the polyploids if Saccharomyces cerevisiae have been studied in detail, and this work has concentrated mainly on gene seglegation rather than gene expression (Lindegren and Lindegren, 1951;Roman et al-, 1955;Leupold, 1956) though more recent papers have studied the eftect of ploidy on mating type (Duntze et al,L97O). This paper reports methods developed for the synthesis and identification of polyploids of kno*tr genotype.…”

Breeding of Bakers' Yeast-Determination of the Ploidy and an Attempt to Improve Practical Properties

“…On the other hand, heterothallic diploid yeasts, homozygous for mating type are reported to be positive in mass mating reaction but negative in sporulation (Roman et al 1951, Lindegren and Lindegren 1951, Pomper 1952, unlike homothallic diploid yeasts. Therefore, on further assuming that the above maters are diploids of mating types as and aca, the results in Table 1 are classified into three tetrad types : (1) 4aa, (2) 2aa : 2aa, and (3) as : as : 2aa.…”

“…(Takahashi 1958) and heterothallic factors (Lindegren and Lindegren 1943) in the parent strain ; (2) segregation of polyploid yeasts heterozygous for mating type (Roman et at. 1951, Lindegren and Lindegren 1951, Pomper 1952, Pomper et at. 1954, Roman et at.…”