Science!: Chickens, Musclefish and X-Ray Vision

Lauren Admire | 15 Mar 2010 21:00

Chickens Have Gender Identity Issues

If you would, please direct your attention to the picture of the odd-looking chicken to the right. Note the differences between the light and dark side of the chicken. The left side of the chicken has a larger wattle, bigger breast and a leg spur, which is evidence of a male hen, called a cockerel. The other side shows all the characteristics of a female hen. This is called a "gynandromorphous" chicken, meaning it is part hen, part cockerel.

In mammals, sex is typically determined by the presence of a gene on the Y chromosome and the influence of hormones that instruct cells to become ovaries or testes. This system was believed to be consistent throughout all vertebrate species. However, the presence of gynandromorphous chickens gave researchers Michael Clinton, Debiao Zhao and Derek McBrid pause.

"We assumed [the gynandromorphy] was caused by one side of the body having some kind of sex chromosome anomaly," states Clinton, a developmental biologist at the University of Edinburgh. "But when we looked at them closely, they were composed of entirely normal cells. We realized that birds don't follow the mammalian model."
Instead of a chromosomal anomaly, researchers found that the bird's cells were completely normal, except that all the male cells lined up to one side, and all the female cells went to the other, resulting in the strange duality in the appearance of the chickens. Hormones didn't play a role in the gender identity of bird cells at all - each cell retained its own gender identity.

To test this theory, researchers planted male cells into a female embryo, and female cells into a male embryo. If hormones played a role in cell sexual identity, these cells would have changed depending on the sex of the embryo they were placed in. However, the male cells remained male, and the female cells remained female, despite being placed in an opposite gender embryo.

"We believe now that certainly all birds, and possibly lower vertebrates will have a cellular identity," Clinton explains. "Remnants of this cellular system may still exist in mammals, but it's overridden by the effects of hormones."

Source: Wired


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