GENE CONVERSION 26-10 



one gene to its allele in the heterozygous condition. At one time I 

 held the view that the fermenter character was maintained by a 

 cytoplasmic mechanism, independent of the gene and could be per- 

 petuated in the cytoplasm of the recessive nonfermenter by inter- 

 action between substrate and cjrtoplasm. If such were the case, 

 fusion of cytoplasms during copulation could establish the factor in 

 the hybrid cytoplasm and it could be transmitted to varying numbers 

 of spores when these were cut out at sporulation from the mixed 

 cytoplasm. If the number of cytoplasmic units were large, nearly 

 all the progeny would be fermenters; if the number small, only a 

 few would acquire the character. This view grew out of some joint 

 work with Dr. Spiegelman in our laboratory. 



We (Spiegelman, Lindegren, and Lindegren) published a paper 

 stating that cytoplasmic transfer occurred when mating, meiosis 

 and isolation of the spores of a heterozygous (fermenter/nonfermen- 

 ter) diploid yeast occurred in the continuous presence of the speci- 

 fic substrate. A backcross mating which had previously produced 

 only ME ME me me asci was repeated with the difference that the 

 gametes, the copulating cells, the zygotes, and the sporulating cells 

 were kept constantly in the presence of melibiose. This resulted in 

 6 ME ME ME ME and one ME ME me me ascus; similar matings in 

 the absence of melibiose had produced 10 ME ME me me asci. 



The cultures from the asci containing 4 fermenters each were 

 dissimilated in phosphate buffer in the absence of melibiose for 

 from 7 to 20 days and then tested in the Warburg apparatus for their 

 ability to ferment melibiose. At the same time the ability to fer- 

 ment glucose was also examined. In 4 asci tested, 2 cultures each 

 lost their ability to ferment melibiose while 2 retained it, although 

 all 4 were capable of fermenting glucose. This was taken to indicate 

 that these were cultures containing the recessive gene which had 

 been carrying the enzyme in the cytoplasm. The fermenting cultures 

 were not tested further, although as the experiments below indicate, 

 they might likewise have lost their ability to ferment melibiose. 



We (Spiegelman, Lindegren, and Lindegren) had concluded from 

 the experiments cited above that the presence of melibiose had en- 

 abled a cytoplasmic enzyme to maintain itself and increase in the 

 absence of the specific gene, normally controlling its synthesis, 

 but this conclusion was shown to be untenable by the following ex- 

 periments. 



Our joint paper with Dr. Spiegelman aroused considerable in- 

 terest and when Dr. Michael Doudoroff visited us, he expressed an 

 intense interest to see the experiment reproduced and extended. 

 When he arrived, we were analyzing the matings 557 x 554, and 573 

 X 571. Since all these haplophases had arisen from the rather reg- 

 ular pedigrees shown in Table 26-3 (from matings 260 x 375 and 

 525 X 520) we predicted to him that only regular segregations would 



