Anatomical defects associated with a feathering mutant (Ottawa naked) in domestic fowl

An autosomal recessive mutation (Ottawa naked, nk) that causes abnormal feathering, fusion of the third and fourth toes, and low viability has been reported previously in the chicken. In the present study mutant individuals were examined from three different stocks: the original one in which the mutant was found and two outbred F2 stocks. Defects of the tail region were observed in all mutants from the original stock (20/20) and in 64% (16/25) of the mutants produced from the outcrossed stocks. The severity of the defects ranged from mild distortion and scoliosis of the coccygeal vertebrae to absence of all vertebrae from the lumbosacral level caudad. Forty percent (16/40) of the mutants from the original stock lacked caudal portions of the kidneys to varying degrees. Edematous areas were observed in 22% (15/67) of the embryos examined at 14 days of incubation. Other defects observed in the mutant embryos but not studied in detail are abnormal patterning or absence of scales, absence of the caudal spinal cord in embryos with severe rumplessness, and failure of the three metatarsal bones to fuse into a single element. Since all structures affected in the mutants differentiate primarily from or may be dependent upon the mesoderm, it is suggested that the site of gene action lies within this germ layer. A decrease was observed in both incidence and severity of the various defects following outcrossing, which suggests the presence of modifiers that influence the expression of the trait.