23-6 THE YEAST CELL 



parasitic existence. Lethal genes have been found by Dodge to be 

 carried in Neurospora tetrasperma by this device. The accumula- 

 tion of degenerate alleles in Saccharomycodes is a good example 

 of the value to a species of the interposition of a haplophase in the 

 life cycle and helps to explain why haplophases are still carried in 

 highly evolved plants such as the Spermatophytes. 



Reversion of n to N 



Winge observed in his genetical analysis of S. ludwigii that the 

 lethal locus n occasionally mutated to the dominant normal N allele. 

 This is apparently another example of the repair of a degraded gene 

 by its dominant normal functional allele in the heterozygous condition. 

 The n allele, therefore, resembles the reverting and irregularly seg- 

 regating genes we have found in Saccharomyces rather than the fully 

 degraded alleles usually used in Neurospora genetics. 



