Half-male and half-female chickens studied

EDINBURGH, Scotland, March 15 (UPI) -- Scottish researchers say they've solved a longstanding puzzle -- why some chickens appear to be male on one side of their body and female on the other.

The research involved studying rare naturally occurring chickens with white (male) plumage on one side and brown (female) plumage on the other. It was previously thought sex chromosomes in birds control whether a testis or ovary forms, with sexual traits then being determined by hormones.

But the scientists from The Roslin Institute at the University of Edinburgh identified differences between male and female cells that control the development of sexual traits. The scientists have named the phenomenon, cell autonomous sex identity.

The investigators say their findings, which they describe as scientifically revolutionary in the field, might also be relevant to why males and females differ in behavior and in susceptibility to disease.

"This research has completely overturned what we previously thought about how sexual characteristics were determined in birds. It also means we must now reassess how this developmental process occurs in other organisms," said Michael Clinton, who led the study. "There is already some evidence that organs such as the heart and brain are intrinsically different in males and females and birds may provide a model for understanding the molecular basis for these gender differences."

The study appears in the journal Nature.