Why Sebright males are hen-feathered

A Sebright rooster does not develop the usual pointed male hackle and saddle feathers. A 1984 breeding study by Somes and colleagues examined the mechanism through crosses and measurements of aromatase, the enzyme involved in converting androgens to estrogens. Offspring from a hen-feathered parent stock crossed with ordinary-feathered stock showed increased skin enzyme activity, and the males developed female-type feathering.

The study distinguished the visible trait from its biochemical dosage. Birds with one inherited copy averaged approximately half the elevated enzyme activity of those with two, yet that lower level could still produce the full feathering effect in males. Thus, enzyme activity showed a dosage relationship while the visible hen-feathering behaved dominantly. This distinction is useful when learning genetics: a dominant appearance does not mean that one and two copies have identical biochemical effects. The paper concerns this feathering mechanism, not all aspects of Sebright fertility, health or temperament.