16 



MUTATION AND PLANT BREEDING 



gametes from marked heterozygotes carrying beta and recessive a, 

 among which no alpha exceptions were found. That this particular 

 beta isolate does not carry an adjacent a element is suggested by the 

 absence of a derivatives among over 15,000 offspring from marked 

 compounds carrying the beta isolate in one chromosome and the 

 original A h complex of Ecuador extraction in the other. 



The results of progeny analyses of heterozygotes carrying beta 

 isolate #1 in one chromosome and the beta:alpha complex of A b - 

 Lima, from which it was extracted, in the other, are presented in 

 Table 5. We note that from T and sh marked heterozygotes of this 



Table 5. — Summary of Exceptional Cases from Heterozygotes Involving Beta 



Isolate No. 1 and the Beta: alpha Complex of ^4 b -LiMA from 



which it was Extracted. 



type five co-1 and 17 nco-1 alpha derivatives were obtained. The five 

 recombinants are expected since they represent crossover isolations of 

 the alpha element of the parental /I ''-Lima and carry the recombinant 

 markers predicted from the knowledge that alpha is the distal element 

 in this complex. Our special interest in these data concerns the 17 

 nonrecombinant alpha cases since, according to the mutation 

 hypothesis, they have the constitution /?„ : a and are presumed to 

 have resulted from the mutation of beta to beta in the A h — Lima com- 

 plex. However, since the isolated beta element in the homologue is a 

 replica of that carried in the A b — Lima complex, an equivalent num- 

 ber of mutations of the former to the /?<, level is expected. These 

 would be scored phenotypically as a (colorless) derivatives, and since 

 they should carry the N and sh parental marker combination, they 

 would be expected to fall in the nco-2 registry of Table 5. Contrary to 



