Cases of mimic mutations and secondary mutations in the X-cliromosomt- <'ic. 21 



wing, though not ;is large as the left one, was strikingly largci- than 

 the male wing of ordinary bilateral gynandroinorphs. This distribution 

 of male and female parts in the wing also conforms with the corresponding 

 distribution of singed and not singed bristles on the neighbouring right 

 side of the thorax. 



The gynandromori)h is explained on the eliiiiinatif)n theory (Morgan 

 and Bridges, '19). An egg bearing the Notch 8 chromosome was 

 fertilized by the X sperm carrying the ruby'-^ singed genes. Elimination of 

 the maternal Notch 8 X occured very early in development, leaving the 

 paternal ruby- singed X to determine the character of the male parts. 



female parts male parts 



N8 



X 



X X 



rb^ sn . rb^ sn 



Grynandromorph (?) 1365. 



In Culture 1365 (Table 2), a back-cross of a wild -type female 

 carrying eosin ruby- singed in one of her X-chromosomes and scute 

 echinus cut in the other, to eosin ruby- singed males, a male occured, 

 the left eye of which w^as eosin ruby^ while the color of the right eye 

 was a typical male eosin and not ruby^ (May 31, 1919). The individual 

 was in addition cut. No difference could be observed with regard to 

 the size of the eyes. 



This exceptional individual can not be accounted for on basis of 

 the elimination hypothesis. The simplest explanation is that of a 

 secundary somatic mutation — that the ruby^ gene of the cell that gave 

 rise to the right eye reverted to not-ruby^. On the hypothesis of a 

 binucleated egg (Morgan and Bridges '19), one nucleus after reduction 

 contained an eosin ruby^ cut X, due to a crossing-over between ruby^ 

 and cut, the other an eosin cut X resulting from a crossing- over 

 between echinus and ruby-. P^ach of the nuclei was fertilized by a 

 Y sperm. 



left side right side 



w^ rb^ ct W^ _ct^ ^ 



Y. 



