Mi 



GENETICS IN RELATION TO AGRICULTURE 



the segregation is in the ratio 9 rough black: 3 rough white: 3 smooth 

 black : 1 smooth white. These relations are shown diagrammatically 

 in Fig. 40. The factor relations are very simple. The genetic constitu- 

 tion of the smooth black race is rrCC and of the rough white race RRcc, 

 where R is a factor for rough coat and its allelomorph r a factor for 

 smooth coat, and C and c are factors for colored and albino coat respec- 



Fio. 40. Results of crossing smooth black and rough white guinea-pigs. Fi is rough 

 black. Ft is in the ratio 9 rough black : 3 rough white : 3 smooth black : 1 smooth white. 

 (After Baur.) 



lively. The FI RrCc is rough black because of the dominance of these 

 two characters over their allelomorphs. When FI individuals are bred 

 together the F 2 segregates in accordance with normal dihybrid expecta- 

 tions as shown in the checkerboard in Fig. 41. 



This experiment shows how easily new races may be established, for 

 in Fz two entirely new combinations of characters were obtained, namely, 

 rough black and smooth white. Of the rough black individuals only 



