THE METHOD OF CYTOLOGY 



475 



of chromosomes; while the work of Miss Carothers furnished evi- 

 dence of their independent segregation during maturation. 



If the example of mono-hybridism between a gray and white 

 mouse be analyzed according to this theory, the assumption is 

 that the zygote from which the gray mouse developed contained 



Zygotes from 

 which Pj 

 developed 



Gametes of 

 P, after 

 maturation 



Zygotes from 

 which Fj gray 

 hybrids de- 

 velop 



Gametes of 



Zygotes from 

 which V> gen- 

 eration de- 

 velops 



1 Homozygous Gray : 2 Heterozygous Gray : 1 Homozygous White 



Fig. 252. — Diagram illustrating independent segregation and possible recom- 

 binations of a single pair of chromosomes bearing a single pair of genes in a 

 case of mono-hybridization between a homozygous gray mouse and a homo- 

 zygous white mouse (c/. Fig. 245). 



G, gene for gray coat-color; W, gene for white coat color. 



two genes for grayness, one from each of its parents, while the 

 zygote from which the v.'hite mouse developed contained two genes 

 for whiteness, one from each of its parents (Fig. 252). Each gene 

 is regarded as being carried in a separate chromosome, but the two 

 genes of each animal are resident in similar chromosomes, forming 

 a pair. At the time of reduction the members of a pair of chromo- 

 somes separate and pass into different gametes. • All the gametes 



