Inheritance of the henny-feathering trait of the sebright bantam chicken

The henny-feathering trait of the Sebright bantam chicken is the result of an enhanced rate of estrogen synthesis (aromatase activity) in skin and other peripheral tissues of this bird. To gain insight into the underlying nature of this mutation, we examined the inheritance of this trait using a sensitive isotopic assay for aromatase activity. All birds of the F₁ generation obtained by crossing homozygous henny X non-henny chickens expressed increased arornatase in the skin, and the males exhibited benny-feathering plumage. The average rate of aromatase activity in the skin of F₁ chicks was approximately half that of homozygous henny chicks. The distribution of increased aromatase activity in the F₂ generation and in the backcrosses of F₁ to the two types of parental strains suggest that the enzyme activity in extragonadal tissues is regulated predominantly by one autosomal gene. Attempts to demonstrate linkage to several known loci by backcrossing F₁ heterozygotes with parental chickens carrying a variety of genetic markers were unsuccessful. We conclude that the enhanced estrogen synthesis in extragonadal tissues in chickens carrying this gene is inherited as an autosomal codominant but that a half maximal level of the enzyme is sufflcient to allow full development of female feathering in affected male birds so that benny-feathering is transmitted as a dominant trait.