500 



The Determination of Sex 



Fu / xb fu X ocb fu, a 9 : 1 : 1 : 9 ratio will also be found among 

 the diploid wasps. These sex-linked ratios lend great support to 

 the explanation based on complementary genes. 



If the cross is an outcross (that is, if the male carries an allele 

 not present in the female), the ju gene will still be linked with 



Fig. 143. A fused female of Hahrobracon juglandis. The short antennae, 

 tarsi and palpi with segments fused together, and the indentation near the 

 tip of the costal margin of the primary wing are characteristic of the 

 fused mutant and segregate together as a single hereditary unit. (Courtesy, 

 Dr. P. W. Whiting in the Journal of Heredity.) 



the X alleles, but such linkage will be masked. In the cross 

 xa Fu / xb fu X ^c fu, all the diploid offspring will be fen^ale and 

 will segregate into 



9 nonfused females 

 1 fused female 

 1 nonfused female 

 9 fused females 



>crossovers 



xa Fu / xc fu 

 xa fu I xc fu\^ 

 xb Fu / xc fiv 

 xb fu I xc fu 



Half the females will be wild type and half will be fused; there- 

 fore, there will be no evidence to indicate that the fused gene is 

 sex linked. The same result would be obtained from the cross 

 xb Fu / xafuX xc fu. 



The first clue to the presence of complementary genes as sex 

 determiners was afforded by the study of certain haploid males. 



