Genetics of scoliosis in chickens.

The genetics of an inherited form of scoliosis in chickens was studied to estimate the number of genes involved, whether they are autosomal or sex-linked, their degree of dominance and penetrance, and the heritability of this trait in this population. Expression of scoliosis and in the progeny was analyzed by radiographs of birds 12 weeks of age or older. Crosses between an inbred line selected for scoliosis expression (incidence of scoliosis - 89 percent) and a highly inbred line displaying normal spinal development provided data for genetic analyses. The incidence of expression of scoliotic parent line implicates three major autosomal, recessive genes. The significantly higher incidence of severe scoliosis found in the homogametic male sex is ascribed to a sex-influenced, on the scoliosis trait rather than to sex-linkage. Variation of expression observed in the scoliotic line is attributed to incomplete penetrance of the major genes, additive effects of minor modifying genes, and primarily to environmental effects. Because of the similarities in the expression of this disease in chickens and humans, the inheritance pattern determined for chickens may provide useful insights into that operating for so-called adolescent idiopathic scoliosis in humans.