4 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. 



tion, because it never fully showed itself in F^ and F,. Nevertheless, in 

 related individuals, the condition is fuUy dominant. We thus get the 

 notion that a factor that normally tends to the development of a character 

 may, although present, fail to develop the character. Dominance is lacking 

 through impotence. 



The last term of the series is seen in the wingless cock which left no 

 wingless offspring in the Fi and F, generations. IeP comparison with the 

 results gained with the rumpless cock, winglessness in this strain is prob- 

 ably dominant but impotent. 



When a character, instead of being simply present or absent, is capable 

 of infinite gradations, inheritance seems often to be blending and without 

 segregation. Two cases of this sort — booting and nostril-height — are 

 examined, and by the aid of the principle of imperfect dominance the 

 apparent blending is shown to foUow the principle of segregation. Booting 

 is controlled by a dominant inhibiting factor that varies greatly in potency, 

 and nostril-height is controlled by an inhibiting factor that stops the over- 

 growth of the nasal flap which produces the narrow nostril. 



The extracted dominants show great variability in their progeny, but 

 the extracted recessives show practically none. This is because a positive 

 character may fail to develop; but an absent character can not develop 

 even a little way. The difference in variability of the offspring of two 

 extracted recessives and two extracted dominants is the best criterion by 

 which they may be distinguished, or by which the presence (as opposed to 

 the absence) of a factor may be determined. 



The crest of fowl receives especial attention as an example of a char- 

 acter preAdously regarded as simple but now known to comprise two and 

 probably more factors — a factor for erectness, one for growth, and prob- 

 ably one or more that determine the restriction or extension of the crested 

 area. 



The direction of lop of the single comb is an interesting example of a 

 character that seems to be undetermined by heredity. In this it agrees 

 with numerous right and left handed characters. It is not improbable 

 that the character is determined by a complex of causes, so that many inde- 

 pendent factors are involved. 



A series of studies is presented on the inheritance of plumage color. 

 It is shown that each type of bird has a gametic formula that is constant 

 for the type and which can be used with success to predict the outcome of 

 particular combinations. New combinations of color and "reversions" 

 receive an easy explanation by the use of these factors. The cases of blue, 

 spangled, and barred fowl are shown also to contain mottUng or spangling 

 factors. 



