SEX-CHBOMOSOMES AND INHERITANCE 175 



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

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

 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 QL 



GRQSSULARIATA d CC 



O (DGER1CELLS0 



GR0SSULAR1ATA90G 



eROSaJLARlATA_d_LG 



O ® GERM CELLS,. ® 



o' ©"" o ®' ® ® "® ■® 



LACTICOLOR 9 OL GR0SSULAR1ATA90C CROSSULARlATAd a GROSSULARIATA d GC 



FiQ. 74. — Cross between Abraxas lacticolor female and groaaulariata 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 



