130 THE FIRST PRINCIPLES OF HEREDITY 



four visible types of individuals in the following propor- 

 tions : F2= 9 AB + 3 A6 + 3 «B + 1 a&. 



It will be seen on closer examination that out of the 

 nine AB, only one is a pure dominant, having the characters 

 ABAB, and therefore breeding true. All the others, though 

 they look like the dominant, contain a recessive character 

 in addition, either a ov b ov both together, and are therefore 

 impure dominants. Of the three A^, one AbAb is pure, 

 while the other two have <? as a recessive. Of the three «B, 

 one is a pure aBoB ; the other two contain ^ as a recessive. 



A/ellowUg 

 '5 rcxind ) 



a green ^ ^^ 

 b angular 



1 ^^2/ 2/ M 1/ 2 



oaionon#B n n 



ABAB AB 



6 



aB AB 



Ab A B 



a b Ab 



Ab Ablab aB aB aB ab ab lab 



D 



sB aB aB ab ablab 



Fig. 53. — DiHYBRiDiSM. (After Lotsy.) 



Lastly, abab is a pure recessive. It foUows from this that, 

 on further inbreeding of the above four types (each 

 separately), we get in the F3 generation one true-breeding 

 line from each — viz., ABAB, oBdB, AbAb, and abab — 

 while aU the others, being impure strains, will, on further 

 breeding, shov/ the phenomenon of segregation. 



One more most important result can be seen to flow 

 from this fact. We started with two pure types — viz. 

 AB, yellow and round, and ab, green and angular. Now 



