Scientists separate the cocks from the chicks

A PUZZLE that has baffled scientists for centuries – why some chickens appear to be half male and half female – has been solved by researchers in Edinburgh.

The research, which involved studying rare naturally occurring chickens with white (male) plumage on one side of the body and brown (female) plumage on the other, sheds new light on the sexual development of birds.

It was previously thought that sex chromosomes in birds controlled whether a testis or ovary formed, with sexual traits then determined by hormones.

The researchers, however, identified differences between male and female cells that control the development of sexual traits.

The study from the Roslin Institute at Edinburgh University is published in the journal Nature.

Dr Michael Clinton, who led the study, said: "This research has completely overturned what we previously thought about how sexual characteristics were determined in birds.

"We now believe that the major factors determining sexual development are built into male and female cells, and derive from basic differences in how sex chromosome genes are expressed."