The sebright bantam chicken and the genetic control of extraglandular aromatase

No ASPECT of sexual dimorphism is more striking or more variable among species than is the feathering pattern of birds. One such sexual difference involves the morphology of feathers. For example, in some birds the feathers of the male are longer and more deeply fringed than those of the female.¹ Species in which such sexual differences are extreme include the lyre bird, the peacock, some types of hummingbird, and the domestic chicken (1). Owing to their accessibility, chickens have been the favored subjects for the study of relationships between gonadal function and feather structure, and it is customary to characterize the plumage of adult chickens as either henny or cocky (Fig. 1) (3). In the hen most feathers are short and straight and have a solid vane with many barbules and hence little fringing. In the rooster, in contrast, the neck hackle feathers, the feathers of the saddle (the median tail coverts), and the major tail coverts and great sickle feathers of the tail are long and deeply fringed owing to the paucity of barbules on the distal ends of the feather barbs.