A group of researchers has detected a gene in a Japanese freshwater fish that determines male sex, according to the group’s thesis published Monday in Nature magazine.

While the sex-determining gene has been identified in most mammals, this is the first time the gene has been detected in nonmammalian vertebrates, the group said.

Consisting of researchers from the National Institute for Basic Biology and several universities, including Niigata University, the group initially analyzed an embryo of a “medaka” fish with a Y chromosome, which usually leads to male sex, and found that a gene, DMY, functioned during sexual differentiation.

The group then found naturally occurring mutations that had female characteristics as well as DMY.

Further research found that these mutations failed to develop male characteristics due to an abnormality in their DMY, leading the group to determine DMY is the male sex-determining gene for medaka.

The group plans to look into whether DMY works as a sex-determining gene for other fish.

Professor Yoshitaka Nagahama of the institute, a part of the Okazaki National Research Institutes, said he expects the research into the sexual differentiation of medaka to ultimately clarify questions surrounding sexual differentiation in human beings.

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