CHAPTER XV 



TJNIT-CHAKACTERS IN POULTRY AND IN PLANTS 



Poultry. The production of varieties by unit-character 

 variation is nowhere more clearly seen than among domestic 

 fowls. The wild ancestor is supposed to be represented at 

 present in the jungle fowl of India (Gallus hankiva) a small 

 bird of bantam size having the color character of the breed 

 known as brown Leghorn, and producing fully fertile off- 

 spring in crosses with domestic breeds. 



Under long centuries of domestication size in many breeds 

 has been increased, though certain breeds of bantams are no 

 larger than the jungle fowl. Punnett and Bailey (1914) have 

 maintained that several unit factors are concerned in size 

 differences between bantam and ordinary breeds, but there 

 is some doubt as to the correctness of their interpretation. 

 We have no information at present as to whether the bantam 

 represents the persistent small size of the wild ancestor or has 

 resulted from secondary variation in races of normal size. 

 The size changes from the wild jungle fowl to our large 

 breeds of poultry have undoubtedly been numerous and 

 probably gradual, involving long-continued selection. 



Color variations are in fowls, as among mammals, the most 

 conspicuous unit-character changes. The plumage of the 

 jungle fowl contains both black and yellow pigments com- 

 bined in a pattern of some complexity. This pattern may 

 possibly be lost or suppressed as a unit-character variation, 

 but in most cases it is changes in the relative amounts of 

 black and yellow which give rise to self black or self yellow 

 (red or buff) breeds. Wliite spotting may come in to produce 

 colorless patches in the ])lumage and if these become suffi- 

 ciently extensive an all-white breed results such as the white 

 Leghorn. The white of Leghorns is a dominant character 



14S 



