THE GENETICS OF HABROBRACON JUGLANDIS ASHMEAD 



They are necessarily associated with haploid 

 parthenogenesis, and consist of many genes de- 

 termining the numerous sex differences, struc- 

 tural, functional, and behavioristic , charac- 

 terizi'ng Hymenoptera. These genes have, in the 

 aggregate, duplicate effects such that all hap- 

 loids or homozygous diploids are similar and 

 male, but combinations of any two different al- 

 leles result in females (heterozygous domi- 

 nants), likewise all similar. 



This principle of sex determination may be 

 illustrated by the foilov/ing example. An xa/xb 

 female homozygous for the autosomal recessive 

 gene, veinless, but heterozygous for fused and 

 having fused associated with xb may be crossed 

 with a non-veinless xb fused male (Fig. 16A). 

 The recessive veinless serves to mark the hap- 

 loid sons which are fused and non-fused in equal 

 numbers. The diploid offspring, whether males 

 or females, will be non-veinless. Among the 

 daughters, xa/xb, the non-crossovers will be 

 wild-type, the crossovers fused, but among the 

 diploid sons, xb/xb, the reverse condition ex- 

 ists. Since crossing over between x and fused 

 is about ten per cent, fused will show great 

 deficiency among the daughters, great excess 

 among the diploid sons. If both parents have 

 fused associated with xa, the offspring occur 

 in the same ratio (Fig. 16B) , but if fused is 

 associated with xa in one parent and with xb in 

 the other, the ratios of fused among the two 

 types of diploid offspring are reversed (Fig. 

 16C and D) giving an excess of fused among the 

 daughters, deficiency among the sons. Thus 

 there are four different arrangements possible 



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