ITI 1 The Breda Comb 67 



Mr Hurst suggested to us that an excellent confirmation 

 of the truth of the analytical method by which the composi- 

 tion of the rose and pea combs has been represented could 

 be obtained by a cross between the rose comb and the 

 Breda, which, as has been stated, has the bifidity-factor but 

 practically no comb at all. The elements involved are 



Rose, R. No rose, r. 



Comb present, C. Comb absent, c. 



Bifidity, B. No bifidity, b. 



The F l generation has the composition Rr, Cc, Bb, 

 namely a double rose comb. F z generation contains a great 

 variety of forms, of which those having B and C, but no R, 

 have the high bifid comb like that of the F^ raised in the 

 cross Breda x Single, and those which contain only r and b 

 in combination with C have single combs of the ordinary 

 high type (Fig. 12). Both these kinds occurred in F^ and 

 their appearance is entirely confirmatory of the scheme of 

 representation adopted. Since neither the rose nor the 

 Breda have outwardly any suggestion of single comb in 

 their appearance, were it not for a knowledge of Mendelian 

 analysis such a result must have seemed utterly unaccount- 

 able. 



When therefore we look at such an organ as the comb 

 of a fowl and attempt to conceive its genetic properties, we 

 have to remember that the structure as a whole may be 

 composite in origin, and that the visible appearances and 

 properties may result from the interaction of a number of 

 distinct elements each transmitted independently in gameto- 

 genesis. 



Everything however points to the conclusion that the 

 number of these elements is finite, and that their properties 

 are not beyond the reach of orderly analysis. 



In the example of the walnut combs the interaction of 

 two dominant factors is such that the 9 members of the F z 

 series of 16 have a feature, the walnut comb, distinct from 

 those of the original parents, while the i member of the 

 series which contains neither dominant factor, also has a 

 feature, the single comb, distinct from anything visibly 



52 



