SEX-CHROMOSOMES AND INHERITANCE 175 



If the sex-chromosome that carries the sex-linked genes 

 in birds and moths be symbolized by Z, and its homologiie 

 that occurs in the female by W, the scheme for sex-deter- 

 mination is that shown in Fig. 73 : The eggs of the female 

 extrude either one or the other sex-chromosome. If Z 

 stays in, and this egg is fertilized by a sperm (Z-bearing 



LACTICOLOR 9 OL 



GROSSULARIATA 6 CG 



® GERM CEaS ® 



GR0SSULAR^TA9 0G 



GROSSULARIATA d LG 



O ® GERn CELLS , (l) (g) 



O ©'" 



LACTICOLOR 9 OL 



O ® 



GR0SSULAR1ATA90G 



® ® 



GROSSULARIATA dCL 



® ® 



GROSSULARIATA 6 CC 



Fig. 74. — Cross between Abraxas lacticolor female and grossulariata male. 



also) a male {ZZ) is produced; if W stays in, and the egg 

 is fertilized by a Z-bearing sperm, a female (WZ) is 

 produced. The way in which sex-linked characters are 

 transmitted may be illustrated by the inheritance of a 

 color difference in the currant moth Abraxas. The wild 

 species (grossulariata) has a mutational variety called 

 lacticolor, that differs from the former by having less 



