Full text: Problems in eugenics

72Exhibit M 6a—7A. 
M 6b 
M 7aDark axil Ï f Light axil 
Sterile J * t Fertile 
Fi Dark axil 
Fertile 
Fa Dark axil Dark axil Light axil f*Light axill 
Fertile Sterile Fertile [ Sterile J 
Approxi- ; *■ 2 1 1 
mate ratio* Not yet found, but probably occurs very rarely. 
(B) If, however, both of the dominant characters go in with one 
parent, and neither with the other parent, they tend to remain 
associated in F,; thus :— 
Light I f Dark 
Sterile} X [Fertile 
F, Dark Fertile 
F2 Dark Dark Light Light 
Fertile Sterile Fertile Sterile 
Ratio. 737 31 3i 225 
In such a cross the classes resembling the two original parents 
tend to be produced in excess, while the other two combinations are 
produced much more rarely. Nevertheless, the ratio of dark to light 
axil, and of fertile to sterile anthers, is, in each case, a simple 3 : 1 
ratio.Example of association of characters in heredity. 
Purple flower colour is dominant to red in the sweet pea, and the 
old-fashioned erect form of standard with the central notch is dominant 
to the hooded. In families where these characters are involved, the 
nature of the F2 generation depends upon the manner in which the 
cross was made. 
(A) When one dominant character goes in with each parent. 
Purple) (Red 
hood J (erect 
Purple erect 
I I I I 
Purple Purple Red | *Red^ 
erect hood erect I hood J 
Approxi- 2 , x 
mate ratio . . 
* Not yet found in this mating, but probably occurs very rarely.
	        

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