BOOTING. 47 



report of 1906. On this hypothesis the offspring with no boot illustrate 

 imperfection of dominance, and one would say that, in booting, dominance 

 is very imperfect. 



However plausible such an interpretation might appear when based 

 on the first hybrid generation alone, it becomes untenable when subsequent 

 generations are taken into account, as we shall see later. The hypothesis 

 breaks down completely in the second hybrid generation and we are forced 

 to the opposite hypothesis, namely, that the clean-shanked condition is 

 dominant. Such an hypothesis would seem, at first, to contravene the 

 principle enunciated in my report of 1906 that the more progressive condi- 

 tion is dominant over the less progressive condition, or absence. But such 

 is not necessarily the fact. We have no right to assume that presence of 

 boot is the new character. The rest of the body of poultry (save the head) 

 is covered with feathers. If the foot is not it must be because there is 

 something in the skin of the foot that inhibits the development of feathers 

 there. And this inhibiting factor is dominant over its absence. 



Table 33 shows that the Silkie crosses yield an exceptionally high per 

 cent of the dominant clear-footed condition. This is additional evidence 

 that the Silkies are DR, and so this cross produces 50 per cent of pure 

 extracted dominants in addition to 50 per cent of heterozygotes in booting. 



To get further light on the nature of inheritance of booting we pass to 

 the examination of the second hybrid generation (table 34). 



In the case of Silkies, which throw 67.6 per cent clean-shanked progeny 

 in Fi, we find in Fj only about 60 per cent clean-shanked. This diminution 

 is, of course, due to the extraction of some pure booted recessives, which 

 draw from the proportion of clean shanks. 



In the case of the Cochins and Dark Brahmas, expectation, with per- 

 fect dominance, is that 75 per cent of the offspring shall be clean-shanked. 

 Since dominance is imperfect (as shown by the occurrence of many booted 

 birds in Fj) we should look for an actual failure to reach so large a propor- 

 tion, but we are hardly prepared for the result that in most of the F^ crosses 

 of Cochins and Brahmas less than 25 per cent of the offspring are clean- 

 shanked. In 4 pens the average is only 10 to 12 per cent, and in one only 

 2 per cent of the offspring fail to develop feathers on the feet. What shall 

 we say of such a case as the last? The history of the father (No. 666) is 

 absolutely certain; his mother was No. 121, the original Dark Brahma 

 female, with a boot of grade 9 and a record in her immediate progeny that 

 indicates perfect purity of booting in her genn-cells. His father was a 

 WTiite Leghorn with clean shanks and without a suspicion of having such 

 antipodal blood as the Asiatic in his ancestry. No. 666 is certainly heterozy- 

 gous in boot, if boot is a single unit. The hens with which No. 666 were 

 mated were clearly heterozygous, as is known not only from their ancestry, 

 but also from their behavior when mated with another cock. No. 254, in 

 which case they threw 12 per cent non-booted offspring. If now both parents 



