Full text: Problems in eugenics

Exhibit M 4—6a. 7 1 
Experiment with Sweet Peas, illustrating reversion on crossing, M 4 
followed by the appearance of numerous types in next generation. 
White x White 
! 
F. Purple 
F, 3 types of purple 3 corresponding figures Whites 
viz :— of reds, viz. :— 
(a) Purple (a) Painted Lady 
(b) Deep Purple (b) Miss Hunt 
(c) Picotee (c) Tinged White 
The varied forms in the F2 generation appear in definite proportions 
and a certain number of plants of each variety are already “ fixed,” and 
have been shewn, by further experiment, to breed true to type. 
Experiment with Sweet Peas, illustrating reversion in structural M 5 
characters. A cross between the ordinary “ Cupid ” dwarfs and the half-dwarf 
“ Bush ” form results in a complete reversion to the normal tall habit 
such as occurs in the wild sweet pea. A further generation raised from 
these reversionary tails consists of tails, Bush, Cupids, and a new form, 
the “ Bush-Cupid.” These last combine the erect bush-like habit of 
growth with the dwarfness of the Cupid. 
Bush x Cupid 
I 
Ft Tall 
F2 J all Bush Cupid Bush-Cupid 
In the 
ratio 9 3 3 1 
Example of association of characters in heredity. M 6a 
In the sweet pea the dark reddish purple axil is dominant to the 
light green one. Also the fertile condition of the anthers is dominant 
to the contabescent sterile condition. In families which involve these 
characters, the nature of the F„ generation depends upon the way in 
which the original cross was made. (A) When each parent has one 
of the dominant characters.
	        

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