Scientists have often wondered why some chickens seem to have male plumage on one side of the body and female plumage on the other. Why exactly are half brown (female) and half white (male) birds strutting around the farm? But reports that scientists may have found an answer to this barnyard mystery. Researchers have found that, unlike in mammals, cells and not hormones dictate sex in chickens. 

It was once thought that sex chromosomes in birds control whether a testis or ovary forms. Further, it was believed that hormones controlled the change. This is how it works in mammals, where hormones control whether testes or ovaries will develop. When biologists first began studying the funky chickens, they thought they might find a chromosomal malfunction. Half-female and half-male chickens are known as gynandromorphs and generally exist in one out of 10,000 birds. But the two-toned chickens were determined to be completely normal. Instead, their gender was already built into their cells.

The study took place at the University of Edinburgh, where Michael Clinton is a developmental biologist. He is co-author of the hermaphrochicken study. According to Clinton, “We assumed this was caused by one side of the body having some kind of sex chromosome anomaly … but when we looked at them closely, they were composed of entirely normal cells. We realized that birds don’t follow the mammalian model.”

Clinton and his team tested their theory by transplanting female cells into a male embryo and vice versa. Regardless of hormonal influences, the cells continued to express their sex-specific hormones. Their sexual determination was cell-based and could not be changed.

Experts say this discovery might also explain why males and females vary in how they handle diseases and behavioral situations. reports that this new discovery could “lead to improvements in poultry production — identification of some of the molecular differences between male and female cells should lead to better tests for sexing embryos prior to hatch.” Some also say that knowing these animals on a cellular level could improve productivity in terms of food production.

For further reading:

Mystery of half-female, half-male chickens solved
Scientists discover that hermaphrochickens exist because of cellular differences -- not because of hormonal influences as is the case with mammals.