Radiography showing the penile bone the clitoris of a French Bulldog.FACULTY OF VETERINARY MEDICINE, UNIVERSITE DE MONTREAL

Though hermaphroditic mammals are not unheard of, most examples of females with testicles are traced to the presence of the SRY gene, normally carried on the Y chromosome and the trigger for the development of male sex traits. But Bijou the French bulldog has no Y chromosome, and no SRY gene, according to researchers at the Université de Montréal Faculty of Veterinary Medicine, marking only the second French bulldog in the world diagnosed with such a condition.

She has a normal vagina and normal uterus, but a disproportionately large clitoris with a baculum (or penile bone), testicles instead of ovaries, and tissue that resembles an un developed prostate.

“She is a female with two X chromosomes and testicles despite the absence of the SRY gene,” David Silversides, the researcher who diagnosed Bijou...

Similar anomalies have been seen in other animals, including pigs, horses, goats and even some dogs, but the condition is very rare, and only in goats have researchers pinpointed a genetic cause of the abnormalities. Silversides suggests a recessive gene, inherited from both parents, is likely responsible for Bijou's condition, adding that the dog could provide new insights into similar disorders in humans.

For more on the sexual development of gonads, see The Scientist's 2009 feature, "Choosing Sex."

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