LINKAGE 



in length. Carson (1941) introduced three genes, 

 broken, white, and stumpy, in the four possible 

 combinations. Linkage between broken and stumpy 

 gave a crossover value of approximately 25 per 

 cent. While the linkage between stumpy and 

 white gave a crossover value of approximately 

 nine per cent. From these and other data Car- 

 son concluded that broken, stumpy, and white, 

 are arranged on the chromosome in that order. 

 The gene, attenuated, since lost, showed link- 

 age with white with 10 per cent crossing over, 

 and with stumpy with 22 per cent crossing over. 

 Its position, therefore, is to the right of 

 white (Fig. 17). Recent work done by P. W. 

 Whiting shows that v/hite and pellucid are very 

 closely linked, only a few recombinations oc- 

 curring out of several hundred wasps counted. 

 There is also suggestive evidence for linkage 

 between red and white with 41.5 per cent recom- 

 bination (Helsel, 1942). Further breeding tests 

 will be required to substantiate the evidence. 

 If found valid, the known linkage groups will 

 be reduced to three. 



The fourth chromosome, or linkage group four 

 (IV), consists of four known loci and is ap- 

 proximately 63 units in length (P. W. Whiting 

 and Benkert, 1934). The four mutants in this 

 linkage group are shot-veins, small-wings, trun- 

 cated, and maroon, arranged in this order on 

 the chromosome. Shot-veins and small-wings are 

 linked with a crossover value of approximately 

 24 per cent. Matings between shot-veins and 

 truncated show linkage with a crossover value 

 of approximately 12 per cent. Maroon and trun- 

 cated are linked with crossing over approxi- 

 mately 27 per cent. 



109 



