64 



INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. 



even show the typical narrow nostril (fig. B, a). On the other hand, in the 

 narrow-nostriled races I have never obtained anj^ such variation. The most 

 deviation that I have seen from grade 1 is found in my strain of Dark 



Brahma bantams that fre- 

 quently give grade 2. The 

 variability of the high nos- 

 tril, the stability of the low 

 nostril, is prima facie evi- 

 dence that the former is due 

 to the presence of a particu- 

 lar factor and the latter to 

 its absence. 



Next, the heterozygotes 

 of Fj (table 46), may be ap- 

 pealed to ; but they will give 

 no critical answer. For ex- 

 pectation, dominance being 

 imperfect, is that the hybrids 

 will be intermediate, and the 

 result will be the same which- 

 ever extreme grade is taken 

 as dominant. The empirical 

 mode in the distribution of 

 the offspring is at grade 2. 

 This implies much greater 

 imperfection of dominance 

 on the hypothesis that grade 

 10 is dominant than on the 

 hypothesis that grade 1 is 

 dominant; but this very fact 

 supports the former hj'po th- 

 esis, since imperfection of 

 dominance is obviously a 

 feature of the character with 

 which we are dealing. 



The critical test is af- 



Fia. B. Polygons of frequency of grades of "openness" of nostril in lOrdeCl Dy tUC -T j generation 



offspring of various parents, a. Both parents pure bred rlominants; 6, both , . *^ - .-,, -j^ , 



parents extracted dominants; c, one parent heterozygous, the other a domi- (tauleS 4o anU 49). xSy ny- 



nant; d, both parents heterozygous; e, dominant by recessive; /, heterozy- ^ ^ - - 



ROUS by recessive; a, heterozygous by extracted recessive; h, extracted r\nfViPc:iQ '7^ nPT* PPTlf. nf ivtP^ 



recessives; i, heterozygous by dominaat;i, both pareuts second generation pULUKfelb, -U pel l.eilU Ul lllC 



^y^"'^^- offspring are expected to be 



pure ("extracted") recessives, and the same number pure dominants ; and also, 

 by hypothesis, the recessives are massed at or near one grade while the domi- 

 nants are variable. Now, as a matter of fact, the upper 25 per cent range 

 over 5 to 7 grades, while the lower 25 per cent are nearly massed in grade 1 



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