SEX-CHEOMOSOMES 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 



CroSULARlATA c5 CG 



O (T) GERM CEaS (g) 



GR0S5ULAR1ATA 9 OG , 



CRQSaJLARlATA 6 LG 



O ® GERM CELLS , ® ® 



o ©■• 



LACTICOLOR 9 OL 



o ©• 



GR0SSULARIATA90G 



® ® ^® ® 



CROSSULARlATAd GL GR055UU\R1ATA d CO 



Fig. 74. — Cross between Abraxas lacticolor female and grosaulariata 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 



