CHAPTER I. 



THE SPLIT OR Y COMB. 

 A. INTERPRETATION OF THE Y COMB. 



When a bird with a single comb, which may be conveniently symbol- 

 ized as I, is crossed with a bird with a " V " comb such as is seen in the PoUsh 

 race, and may be symbolized as oo, the product is a split or Y comb. This 

 Y comb is a new form. As we do not expect new forms to appear in hybrid- 

 ization, the question arises. How is this Y comb to be interpreted ? Three 

 interpretations seem possible. According to one, the antagonistic char- 

 acters (allelomorphs) are I comb and oo comb, and in the product neither 

 is recessive, but both dominant. The result is a case of particulate inherit- 

 ance the single comb being inherited anteriorly and the oo comb poste- 

 riorly. On tliis interpretation the result is not at all Mendehan. 



According to the second interpretation the hereditary units are not 

 what appear on the surface, but each type of comb contains two factors, 

 of which (in each case) one is positive and the other negative. In the case of 

 the I comb the factors are presence of median element and absence of lateral 

 or paired element ; and in the case of the oo comb the factors are absence of 

 median element and presence of lateral element. On this hypothesis the two 

 positive factors are dominant and the two negative factors are recessive. 



The third hypothesis is intermediate between the others. According 

 to it the germ-cells of the single-combed bird contain a median unit char- 

 acter which is absent in the germ-cells of the Polish or Houdan fowl. This 

 hypothesis supposes further that the absence of the median element is 

 accompanied by a fluctuating quantity of lateral cere, the so-called V comb. 



The spUt comb is obtained whenever the oo comb is crossed with a 

 type containing the median element. Thus, the offspring of a oo comb and 

 a pea comb is a split pea comb, and 

 the offspring of a oo comb and a rose 

 comb is a spUt rose. The three hy- 

 potheses may consequently be tested 

 in three cases where a split comb is 

 produced. 



The first and third hypotheses 

 will give the same statistical result, 



namely, the products of two Y-combed individuals of F^ used as parents, 

 will exhibit the following proportions: median element, 25 per cent; split 

 comb, 50 per cent; and no median element, 25 per cent. These proportions 

 will show themselves, whatever the generation to which the Y-combed 



