10 



INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. 



The single comb recorded in the case of 7 birds is doubtless merely 

 the limiting condition of a Y comb in which the median element is developed 

 to its fullest extent. All but 2 of the 7 were recorded from early embryos 

 when an incipient bifurcation would be more difficult to detect. This 

 explanation applies generally, and accounts for the usual excess of I comb 

 when compared with Y comb, as for instance in table 3, page 7. Return- 

 ing to table 7, it is, consequently, probable that only the Y-combed and 

 non-median-combed offspring are produced and that they are in the pro- 

 portion of 99 to 115 or of 46 per cent to 54 per cent. If we add together all 

 records of a oo X Y cross, disregarding the generation of the parents, we get 

 a total I comb 5,* Y comb 177, oo comb 172, and absent 3, or 182 (51 per 

 cent) with the median element and 175 (49 per cent) without. Thus the 

 00 XY cross gives the 1 : 1 proportion called for on the first and third 

 hypotheses and not at all the variety required by the second hypothesis. 



Table 8. 



Finally, we must consider the result of mating a bird without papillae 

 (No. 1420, pen 704) with a median-combed hen (480). When this typical 

 single-combed hen was used the 49 progeny were all of the Y type.f This 

 proves that the combless type behaves only as an extreme of the non- 

 median type. 



When Y-combed hens were used with the combless cock the offspring 

 had Y comb and non-median-comb in nearly equal numbers, 23 : 27 

 (table 8), but the latter included an unusually large proportion of combless 

 fowl (15 in 27). When a combless hen (No. 4257) was used, 9 of the off- 

 spring had 00 comb and 2 no comb; not a greater proportion of combless 

 birds than in the no-comb X Y-combed cross. All of these facts indicate 

 that "co-.iblessness" is not entire absence of the comb factors, but a mini- 

 mum case of the oo or paired comb. This result is opposed to the second 

 hypothesis. 



The statistics of all matings between I, Y, and no comb on the one 

 side and no comb on the other thus speak unanimously for the conclusion 

 that in these matings we are not deahng with 2 pairs of allelomorphs, but 

 with a single comb and it s absence (third hypothesis) or with a case of 



♦ Excluding 6 doubtful because from too young embryos and not obsenred by myself 

 t One IB reported as having a I comb; probably the limiting condition, again. 



