ADAPTATION TO PANTOTHENATE DEFICIENCY 22-14 



Culture 2154 ( — ) required more than 30 days to adapt to panto- 

 thenate synthesis in Burkholder's medium with no added pantothenate. 

 A culture of 2154 grown for 7 weeks in this medium produced full 

 growth on a second transfer to Burkholder's medium without added 

 pantothenate six days after adaptation. This culture was designated 

 2154 (+ adapted). After several transfers on the deficient medium, 

 this adapted culture and 2113 ( — ) produced fertile asci, six of which 

 were dissected (table 22-1). Pantothenate independence vs. depen- 

 dence segregated 2:2 in each ascus and full growth of the dominants 

 was achieved in between four and eight days revealing that adaptation 

 resulted from mutation of a single gene. 



A control test is always made by inoculating a tube containing 

 pantothenate. This makes it possible to detect cases in which failure 

 to grow is not due only to pantothenate dependence, but to some addi- 

 tional deficiency arising by mutation. Such cultures may be panto- 

 thenate independent but unable to grow due to the effect of the new 

 mutation. The culture marked wjth a single asterisk failed to grow 

 in the control tube containing pantothenate presumably due to its in- 

 ability to synthesize some essential substance not present in Burk- 

 holder's medium. 



Matings of unadapted 2154 (— ) by 2113 (— ), and by 2151 (— ), on 

 the other hand, produced asci which contained only dependent asco- 

 spores. 



In order to determine whether the mutation involved back mu- 

 tation of the recessive allele to the dominant allele of the gene for 

 pantothenate independence, or was a mutation at a new locus, crosses 

 were made between 2154 (+, adapted) and both 2114 (+) and 2152 (+). 

 If two different loci are involved, three kinds of asci may be obtained. 

 If we designate one pair of alleles for independence, as A and a, and 

 the other as B and t, the three types are AB AB ab ab, Ab Ab aB aB, 

 and AB Ab aB ab. Then the first type of ascus listed (AB AB ab ab) 

 will contain two independent and two dependent spores, the next all 

 independent and the last three independent to one dependent. If the 

 genes are freely assorting, these asci will be obtained in a ratio of 

 1:1:4 (Lindegren 1948). 



A hybrid of dominant 2114 {+^) by 2154 (+, adapted) produced 

 three asci each containing three independent ascospores. This is 

 the most frequent type of culture obtained when two freely mating 

 non-allelic genes are hybridized. If 2114 (+) is Ab and 2154 (+, a- 

 dapted) is aB, the double dominant can be indicated by AB, the dou- 

 ble recessive by ab, then the asci are AB Ab aB ab. A mating of 

 2114 (+ ) by 2154 ( — , unadapted) reveals that the original dominant 

 (Ab) stock contains a single independent gene. The mating of 2114 

 (+) by 2115 (+) shows that each carries a single dominant gene, the 

 cross of Ab by Ab producing four Ab dominants in each ascus. A 

 mating of 2154 (+, adapted) by its unadapted sister 2151 ( — ) showed 



