Section 1 — Complex Loci 



use of oyster and scarlet mutations, acting as 

 markers of each pleiotropic gene of the series. 

 Data in full are at present being published in 

 Genetics. 



1.12. Partial Complementation of Six Multiple Alleles 

 in a Chlorophyll Mutation Locus in Barley. 



Gerhard Holm (Lund, Sweden). 



A locus in chromosome 1 contains at least 6 

 recessive vital viridis alleles which, when inter- 

 crossed, give Fi's exhibiting different degrees 

 of partial complementation judging from the 

 visually examined leaf colours. A spectrophoto- 

 metrical analysis of 8 of the Fi's verified this 

 interpretation and also showed that the degree 

 of complementation in an Fi apparently depends 

 upon the relative position in the locus of the 

 two alleles involved in the cross. The 6 alleles 

 probably belong to the same cistron and overlap 

 each other in a linear order. The less two alleles 

 overlap, the higher the complementation in 

 their Fi. 



The pigment content in 5 of the alleles is the 

 same, 1.23 mg/g fresh weight, but in the 6th 

 (no. 4 in the linear order) it is significantly higher, 

 1.44 mg/g fr.w. Normal plants contain 2.00 

 mg/g fr.w. 



The 6 multiple alleles appeared in a material 

 of 82 vital viridis mutations of which the resulting 

 76 most probably belong to single loci. 865 dial- 

 lelic crosses were made in the group and the 

 result indicates a very low frequency of multiple 

 allele loci among the vital viridis mutations. 



1.13. Fine Structure of Genes Conditioning Resistance 

 to Erysiphe graminis hordei at the Ml a 

 Locus in Hordeum vulgare. John G. Mose- 



man (Beltsville, U.S.A.). 



Several genes conditioning the resistant reac- 

 tion of barley Hordeum vulgare L. to infection 

 with the ascomycetous fungus Erysiphe graminis 

 DC. f. sp. hordei Em. Marchal have been found 

 at the Ml a locus on chromosome 5. Genes Ml a , 

 Ml a 2, and Ml a 3 at this locus were studied. When 

 genes Ml a and Ml a 3 were homozygous they 

 conferred a similar degree of resistance, but 

 when heterozygous with a recessive gene condi- 

 tioning susceptibility they conferred a different 

 degree of resistance. Gene Ml a 2 conditioned a 

 lesser degree of resistance than genes Ml a and 

 Ml a 3. The degree of resistance conferred when 

 the genes were Ml a Ml a 2, Ml a Ml a 3. or Ml a 2Ml a 3 

 also was determined. For each gene conditioning 



the reaction of the host, a corresponding gene 

 has been found conditioning the pathogenicity 

 of the pathogen. Pathogenically different cultures 

 differentiated the genes at the MI a locus. The 

 relation of the pathogen genes corresponding to 

 host genes was determined by the pathogenicity 

 of haploid progeny cultures derived from crosses 

 between selected cultures. Pathogen gene A a 

 corresponding to host gene Ml a was inherited 

 independently of pathogen genes A a 2 and A a 3 

 corresponding to host genes Ml a 2 and Ml a 3, 

 respectively. Pathogen genes A a 2 and A a 3 

 were found to be at or near the same locus. The 

 utilization of degree of resistance conferred, 

 relation of corresponding pathogen genes, and 

 other host-pathogen relations in studying fine 

 structure of genes conditioning resistance to 

 E. graminis f. sp. hordei at the Ml a locus in H. 

 vulgare were discussed. 



1.14. Complementation, Recombination, and Biochemi- 

 cal Relationships within the Td locus in Neuro- 

 spora crassa. Ann Matthews LACY(Baltimore, 

 U.S.A.). 



The present study of non-indole-utilizing 

 (NIU) tryptophan synthetase deficient mutants 

 indicates that the complementation and recom- 

 bination maps of the Td locus are not co-linear. 

 The clustering on the recombinational map bears 

 some relationship to the biochemical charac- 

 teristics of the mutants; however, the biochemi- 

 cal relationships between mutants grouped 

 together by complementation appears some- 

 what obscure. 



The twenty NIU complementing mutants 

 tested are distributed among three of the four 

 complementing groups previously established 

 for NIU mutants (the fourth group is still re- 

 presented by Tdl only). 



The ability to form cross-reacting material 

 (CRM) is not a prerequisite for complementa- 

 tion. Four CRM~ mutants are in the Tdl\ 

 complementation group. These mutants, how- 

 ever, are not located near Tdl I on the recombina- 

 tion map, but are located in the vicinity of 

 Tdl, 7, and 24 (i.e. "profound region"). 



The ability to catalyze the formation of indole 

 from indole-glycerolphosphate is not limited to 

 members of the 7^71 complementation group, 

 but can be detected at varying levels in crude 

 extracts of at least 90% of the CRM+ 

 NIU mutants tested (including Td3, 7, and 24). 

 CRM" mutants tested exhibit no detectable 

 activity in this reaction. 



Of three temperature sensitive mutants stud- 

 ied (mutant phenotype at 25°C, not at 37°C), 



