An investigation of the mutant chicken line (DAM) characterized by postnatal amelanosis and serious visual problems will be continued. Developmental studies to determine the onset of the cutaneous and ocular changes will be made using EM and light microscopy. Pathological changes in the choroid, retina and optic nerve will be continued with particular emphasis on relationship to visual status. Additional behavioral studies on partially sighted DAMs will be conducted using a visual acuity-feed locator test using genetic albinos as one of the controls. Bursectomy and thymectomy will be utilized to study the effects of altered T and B lymphocyte numbers on the amelanosis. The tyrosine-tyrosinase status of the amelanotic cutaneous melanocyte will be studied using split feather incubation techniques. In addition, genetic studies will be continued with special attention on the backcross and F3 generations of the new heavier melanized sublines (using fibromelanosis, Fb, and dermal melanin id plus). The main DAM line population will also be studied in respect to the relative incidences of feather amelanosis and visual defects, as well as the frequent thyroid and feather structure abnormalities.