Section 1 — Complex Loci 



mutants were crossed to B5 to determine whether 

 the mutants are identical to B5. In addition, 

 crosses were made to five other pan-2 alleles 

 located at various points on the genetic map of 

 the locus. Two of the mutants map at the same 

 site as B5; however, one of these mutants 

 is a non-complementing type while the other 

 exhibits a different complementation pattern 

 from B5. Fourteen of the mutants are located 

 near B5 in the proximal region of the genetic 

 map. Ten are located near the distal end of 

 the map, while the three others are located at 

 different sites near the middle of the map. 

 The relationship between complementation and 

 genetic maps of primary and secondary mu- 

 tants will be discussed further. 



Supported in part under a contract, AT 

 (30-l)-872, with the U.S. Atomic Energy Com- 



mission. 



1.18. Allelic Recombination and Complementation in 

 Adenine-requiring Mutants of Schizosaccha- 

 romyces pombe. C. Ramirez, J. Friis and U. 

 Leupold (Bern, Switzerland). 



Allelic recombination and complementation 

 have been studied in several groups of mutants 

 blocked in adenine biosynthesis, including two 

 groups accumulating a red pigment (ads and 

 adi) and one group blocked in an early reaction 

 preceding the pigment blocks (adi). 



In the ad-? group, 152 u.v.-induced allelic 

 mutants have been demonstrated to represent 

 mutations at 33 different but closely linked sites, 

 recombination frequencies ranging from 1 to 

 77° prototrophic recombinants per 10 6 as- 

 cospores. The mutant distribution is character- 

 ized by "hot spots", one particular site having 

 contributed as many as 26 per cent of the mu- 

 tants. Complementation has not been observed 

 in any of the pairwise mutant combinations 

 tested. 



In the ad\ group, however, complementation 

 leading to a more or less prototrophic phenotype 

 has been found in many of the diploid combina- 

 tions tested. The complementation pattern of 

 138 mutants of u.v.-induced, diethylsulfate- 

 induced and spontaneous origin may be re- 

 presented by a linear complementation map in 

 which eight types of complementation behaviour 



define five different "complementation units". 

 The complementation and recombination maps 

 show a considerable degree of co-linearity. 



A more complex complementation pattern has 

 been found in allelic combinations of 158 u.v.- 

 induced mutants of the constitution ad§. The 

 results of complementation tests involving 

 21 different types of complementation behaviour 

 may be represented in a complementation map 

 in which both ends are closed to circles. With a 

 few notable exceptions, the complementation 

 and recombination maps show again a sig- 

 nificant degree of co-linearity. 



1.19. Studies on the Genetic Fine Structure of the 

 ad7 and adg loci of Schizosaccharomyces pom- 

 be. H. Gutz (Berlin, Germany). 



Leupold has done a very extensive intragenic 

 recombination analysis in the adi and ad& loci 

 of Schiz. pombe. The ad& locus shows the 

 phenomenon of allelic complementation. In 

 addition to the intragenic recombination analysis 

 Leupold has constructed a complementation 

 map of this locus. All mutants analysed by 

 Leupold have been induced by ultraviolet irradia- 

 tion. The ad- and adz mutants are not randomly 

 distributed in the maps. There are a few "hot 

 spots", and the mutation sites appear to be 

 concentrated in several parts of the map. 



Taking the maps of Leupold as a basis, I 

 have analysed the intragenic distribution and 

 the complementation pattern of mutants which 

 were induced by nitrous acid and X-rays. In 

 both loci (adi and ad&) the intragenic distribu- 

 tion of the nitrous acid-induced mutants is quite 

 different from that of the u. v. -mutants. They 

 show some pronounced "hot spots". Above 

 half of the sites induced by nitrous acid are not 

 present on the u.v.-map. From the non-random 

 distribution of the mutants it is concluded that 

 a direct deamination of the DNA-bases is 

 not to be considered as mutation mechanism. 

 All X-ray mutants map on single sites, and no 

 intragenic deletions have been found. 



According to the results of Leupold, the 

 complementation map of the ade locus is non- 

 linear. Seventy-nine per cent of the nitrous 

 acid-induced mutants show complementation. 

 Among these mutants at least 6 complemen- 

 tation types were found which are not present 

 in the u. v. -mutants. 



