Polyploidy in Yeast and its Bearing on the Occurrence of Irregular Genetic Ratios

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Abstract
The facts that irregular ratios (as phenotypic ratios of 4:0, 3:1. 1:3 and 0:4 in place of the expected segregation of 2:2) appear in asci of Saccharomyces and that evidence for polyploidy in this plant prompted reappraisal of a possible role of the latter interpretation of irregular ratios. One of 64 4-spored linear asci was found which exhibited an irregular ratio for mating type, galactose fermentation, and growth habit in liquid medium. All asci were produced from a cross between two clones presumably haploid and were agf and a GF in constitution. Clones grown from the 4 spores of the exceptional ascus were negative-reacting in mating type and each was self-sporulating. All 4 produced asci in gypsum slants. Twelve asci, 3 from each of the 4 clones, were dissected and tests made. Ten had 4 viable spores and exhibited a 2:2 segregation for both mating type and flaking. Of the remaining 2 asci, only 3 of 4 spores survived but there was observed a segregation for a and a as well as F and f. A disomic condition for at least three chromosomes of the complement, and a probability that each of the spores was actually diploid is inferred.

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