Denticles of all rows display normal arrangement and polarity but they are thin and sinuous ('goose-necked') compared with the stout hooks seen in wild type. The normally stout triangular hairs near the anterior margins of segments exhibit a similar phenotype. Longer hairs are close to normal but typically are not as straight, uniformly tapered and pointed as wild type.

A dominant cis-acting enhancer of the reversion rate of f^3N; thought to be at least partially responsible for reported instability of f^3N. Does not increase the frequency of sex-linked lethal mutations. Has no effect on the reversion frequencies of mutations in v, car, y, w, m, Bx or B.

Expression similar to f but unlike f, does not respond to su(f). Characterized by a high spontaneous reversion rate (~2 x 10^-5); rate may be further increased by a closely linked cis-dominant mutator allele, Mu(f^3N), (5 x; Woodruff, 1975), by X rays (20 x; Green, 1977) and by mustard gas (Woodruff, Bowman and Simmons, 1972). not suppressed by su(f). RK1.