CHAPTER 5 



GENITIC INTERSEXUALITY IN DROSOPHILA, 

 CERTAIN LEPIDOPTERA AND BIRDS 



Drosophila. The first description of a gene in Drosophila 

 which profoundly affected the sexual characterization was 

 that given by Sturtevant (1920) in D. simulans. In a par- 

 ticular stock it was noted that many individuals exhibiting 

 a definite intersexual condition appeared. They were 

 sterile, but the mating of their apparently normal brothers 

 and sisters to unrelated stocks commonly produced the 

 same abnormal forms in the Fg generation, the sex-ratio 

 being of the order of 4 males; 3 females, i intersex, which 

 suggested that these intersexes were modified females. By 

 the use of sex-linked genes Sturtevant was able to demon- 

 strate that this was so, and further breeding experiments 

 showed that the agent responsible was a recessive gene 

 resident in the second chromosome. 



In Drosophila virilis Lebedeff (1934) found a third 

 chromosome recessive gene which transformed the XX 

 individual into a sterile male but left the XY individual 

 unaffected. Later (1937) Lebedeff showed that the XX 

 individual began its development according to the female 

 pattern and that later male organs made their appearance, 

 the two sets, male and female, continuing thereafter to 

 develop side by side. 



Bridges (1921, 1922, 1925) described a form of inter- 

 sexuality in Drosophila melanogaster caused by an altered 

 ratio of sex-chromosomes and autosomes. These intersexes 

 showed complex mixtures of male and female parts. They 

 could be produced by breeding from certain of their sisters 

 which were to be distinguished by their large coarse eyes, 

 thick-set bodies, coarse bristles and hair pattern on the 

 wing. Cytological examination demonstrated that these 

 intersex-producers were triploids, every chromosome being 

 present in triplicate (3N). All the eggs produced by them 



42 



