So just how different are males and females really? Fugu sex determined by single nucleotide

November 7, 2012

The genetic information that determines sex is carried on sex chromosomes, which come in two forms: X and Y. Individuals with two X chromosomes become female while those with one of each become male. The human sex chromosomes differ greatly, the Y chromosome being only one-third of the length of the X chromosome, and the sex-determining genes that regulate the development of the sexual organs are found only on the Y chromosome.

Wild fugu © Naoki Mizuno

Similar differences in DNA sequence have also been confirmed in the mouse, and although researchers were aware that the human sex chromosomes may have been an extreme case, conventional wisdom held that a certain level of difference existed in the sex chromosomes of most vertebrates.

Assistant Professor Kiyoshi Kikuchi and a research team at the Fisheries Laboratory in the University of Tokyo Graduate School of Agricultural and Life Sciences have discovered that layout of genes on the X and Y chromosomes in the fugu (tiger pufferfish) Takifugu rubripes is almost identical, and both have a copy of the “anti-Mullerian hormone receptor type II (Amhr2)” sex-determining gene. Fugu sex is determined by a difference of just one nucleotide between these two copies of Amhr2.

This research result is significant as it shows an extremely simple example of sex determination, demonstrating that the human and mouse sex determination systems are not a universal model for all vertebrates.

Fugu occupies an important place in Japanese cuisine. In addition to this discovery’s significance as a basic research finding, it may lead to the development of a convenient method for determining fugu sex, which will assist in preserving the ecosystem in which fugu live and protecting fugu in the wild.

Department release/press release (Japanese)


Takashi Kamiya, Wataru Kai, Satoshi Tasumi, Ayumi Oka, Takayoshi Matsunaga, Naoki Mizuno, Masashi Fujita, Hiroaki Suetake, Shigenori Suzuki, Sho Hosoya, Sumanty Tohari, Sydney Brenner, Toshiaki Miyadai, Byrappa Venkatesh, Yuzuru Suzuki, Kiyoshi Kikuchi,

“A Trans-Species Missense SNP in Amhr2 Is Associated with Sex Determination in the Tiger Pufferfish, Takifugu rubripes (Fugu),”

PLoS Genetics 8 2012: e1002798, doi:10.1371/journal.pgen.100279

Article link


Graduate School of Agricultural and Life Sciences

Fisheries Laboratory (Japanese)

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