CYTOPLASMIC INHERITANCE 



27-6 



The diploid cells were viable and reproduced vegetatively with- 

 out any obvious deficiencies. However, when they were induced to 

 sporulate and the spores were isolated, only about 2 per cent of 

 them were viable. Winge and Laustsen concluded that the low vi- 

 ability of the ascospores from directly diploidized cells arose from 

 the failure of the cytoplasm to divide before copulation. They sug- 

 gested that the structures in the cytoplasm which fail to divide are 

 chondriosomes or other structures independent of the genome (fig. 

 27-2). 



Fig. 27-2 Diagram copied from Wings and Laustsen explaining 

 their hypothesis of degeneration through inbreeding. 



ADAPTATION WITHOUT DETECTABLE 

 CHANGE OF GENOME 



Illegitimate diploids are genetically stable forms because they 

 sporulate rarely and if transferred frequently in broth, will not 

 sporulate at all. The failure to sporulate eliminates segregation 

 as a cause of variation. The poorly sporulating illegitimate R- 

 strain diploid described in Chapter 6 can be adapted to corn steep 

 water agar which contains an unknown substance that inhibits yeast 

 growth (Lindegren, 1945). 



Malt (M) agar is a relatively complete medium which supports 

 an abundant growth of imiformly large colonies. It contains 10 per 

 cent malt extract, 0.5 per cent dextrose, 0.5 per cent dried yeast, 

 1 per cent CaC03, 3 per cent agar. Corn steep water agar (C) con- 

 tains 0.8 per cent sucrose, 0.7 per cent corn steep water solids, 1 

 per cent CaC03, 3 per cent agar. On the first transfer from M a- 

 gar to C agar only a small percentage of cells survives producing 



