IS 



MUTATION AND PLANT BREEDING 



Table 6. — Summary of Exceptional Cases from Compounds Involving 17 

 Independently Isolated Beta Elements and the ^4 b -Lima Complex. 



Source 



Beta 



isolate 



.4 b -P 



gametes 



tested 



Distribution of alpha and colorless 

 derivatives among the offspring 



nco-1 



nco-2 



co-1 



co-2 



T ,4 b -Lima/N /3-Lima sh 



151-1 

 151-2 

 153-1 

 161-3 

 162-1 

 165-2 

 165-3 

 174-3 

 183-2 



4,580 

 5.945 

 4,470 

 2,650 

 26,475 

 4,670 

 4,620 

 4,135 

 8,945 



1 Ta 

 1 



1 







14 



1 



2 " 

 



1 



Sh 



Totals 



T A h -\Am&/N /3-Cusco sh 



155-5 



155-9 



155-12 



156-3 



168-1 



178-1 



190-2 



280-1 



66,490 21 



2,530 

 8,585 

 7,745 

 8,675 

 5,160 

 8,330 

 6,295 

 1,815 



T aSh 



N a sh 



Totals 



T A h -Uma/N a sh* 



49,135 20 



88,890 31 T a Sh 



A N a Sh 



•These individuals occurred as sibs of the heterozygotes listed above. Data presented in this row 

 represent totals for all such sibs. 



against the gene mutation hypothesis. 



It is appropriate to consider at this point certain other experi- 

 ments designed to test the mutation hypothesis for the origin of the 

 noncrossover alpha cases. These studies, like those reported above, 

 are based on the argument that if gene mutation of the beta element 

 in the complex is responsible for the occurrence of the nonrecom- 

 binant alpha, the latter, represented as /?„ : a (see Figure 2), should 

 carry a null beta form which is susceptible to isolation by crossing 

 over in advanced generation tests of these derivatives. These studies 

 (20), carried out in this laboratory, not only fail to support the gene 

 mutation hypothesis, but provide strong empirical support for the 

 supposition that, if the event in question is not due to a qualitative 



