the homostyle form. When Bateson and Gregory crossed this 

 form with a small eyed thrum form the progeny (Fi) were 

 all small-eyed short -styled, i.e. small-eye (s) is dominant to 

 large-eye (L), and Thrum, T, (short style) to Pin, P. (long 

 style) ; but the " F2 generation consisted of four types, viz., 

 short-sytled with small-eyes, short-styled with large-eyes, 

 long-styled with small-eyes and homostyled with large 

 eyes. The proportions in which these four types appeared, 

 namely 9:3:3:1, show that the presence or absence of but 

 two factors is concerned." Moreover, it suggests that the 

 short-style of the homostyle form is "potentiallv long- 

 styled." 



The gametic formula for the F2 generation may be re- 

 sented as follows: 



Female , 

 Gametes 1 



Result: — 9 Thrum small-eyed forms 

 3 Thrum large-eyed forms 

 3 Pin small-eyed forms 



1 Pin large-eyed, which becomes the homostyled 

 form. 

 (Bateson, Principles of Heredity, p. 70). 



Castle has determined that the grey color of the wild 

 mouse depends on the co-operation of at least six different 

 factors, and that the "agouti" color of the wild rabbit 

 appears on crossing a yellow with a Himalayan variety. 

 The grey color of the ordinary rabbit depends on two factors. 

 Other examples are the commercial carnation, a cross 

 between the single type and the double bull-head; and 

 Emerson's crosses with maize, gourds and beans. 



Early falling, of ripe grain from heads. — 



Mr. Ubisch finds that this character appears in barley 

 as the result of the presence of two Mendelian factors. 

 When either, or both, is absent the defect does not appear. 



Human Characters. — Explain why blue-eyed parents 

 have no brown eyed-children? 



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