The Chicken Frizzle Feather Is Due to an α-Keratin (KRT75) Mutation That Causes a Defective Rachis
Figure 1
The frizzle chicken phenotype.
(A) Diagram of normal developing and mature embryonic and adult chicken feathers. (B) Adult, hatchling and 1-month-old frizzle chickens. Adult homozygous frizzle chicken feathers curve away from the body. This is a frizzle in White Plymouth Rock Bantam, it is not exactly the chicken we use but illustrate the phenotype. Note that the downy feathers appear normal in newborn frizzle chicks; however, by the second generation, the feathers in a one month old chick start to show a clear frizzle phenotype. (C) Comparison of body feathers from normal white leghorns and frizzle chickens. Upper panel: dorsal view, ventral view and side view. Lower panel: dorsal view (left) and ventral view (right) of branching in the pennaceous vane; D, dorsal; V, ventral. (D) Comparison of the wildtype, heterozygous and homozygous frizzle feathers. The wildtype feather image is overlaid by the computer-determined backbones of its rachis. (E) Function θ(s) describing the bending of their rachis, plotted on the length-normalized coordinate. The functions are shifted by arbitrary offsets for clarity. (F) Comparison of the feathers as shown by the qualitative change of the curves of θ(s). Red arrows highlight the kinked structures along the heterozygous feather.