. Carnegie Institution of Washington publication. 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
. Carnegie Institution of Washington publication. 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, bothpareutssecond generation pULUKfelb, -U pel Ul lllC ^y^"'^^- offspring are expected to be pure ("extracted") recessives, and the same number pure dominants; and also, by hypothesis, the recessives are
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