The Use of the Ribonavinless Gene (rd) in Determining the Cause of Clubbed Down

THE term “clubbed down” was first used by Lepkovsky et al. (1938) to describe an abnormal down condition characterized by a buckling of the down plumule within the sheath to give the appearance of a small club. Because the effect was observed in embryos suffering from a riboflavin deficiency, it was postulated that this condition was responsible for the expression of the trait. Subsequent work by Peterson et al. (1947), Coles and Cumber (1955), and Brown (1957) tended to agree that riboflavin deficiency was a factor in the expression of clubbed down. Kabystina and Petrov (1935) reported another down condition in chickens, shortened down, which they found was always associated with black down color. Hutt (1951) found both clubbed and shortened down in the black non-barred female chicks from a Rhode Island Red × Barred Plymouth Rock cross. Hawes and Buss (1963) have found clubbed down associated with extended…