IV] 



Presence and Absence 



77 



Then in the case where grey x albino gives in /% 

 9 grey : 3 black : 4 albino, 



we simply have to regard B, the black determiner, as 

 common to both parents, and the same numerical result 

 is produced. Such a case may usefully be represented in 

 a tabular form, thus : 



Parents Grey x Albino 



Gametic Composition... CGB cgB 



Grey 

 CcGgBB 



! 9 Grey 



3 Black 



12 



3 



i 

 4 Albino 



4 



i 



Fig. 15. Distribution of grey, black, and albino individuals in F z from 

 the cross grey, CGB, with albino cgB, showing the meaning of the 

 ratio 9 grey : 3 black : 4 albino. 



