Japanese researchers have stumbled upon the genetic switch that determines whether germ cells turn into sperm or eggs in vertebrates, a crucial discovery that could help scientists better understand how the reproduction of vertebrate life on Earth happens and how it evolved.

The gene, called foxl3, has been found in small fish called Medaka, or Oryzias latipes, according to a LiveMint report.

Dr. Toshiya Nishimura, along with Associate Professor Minoru Tanaka from the National Institute for Basic Biology, National Institutes of Natural Sciences in Japan and other researchers found that the foxl3 genes suppresses the germ cells from turning into sperm. Females that don’t have foxl3 genes end up with a fish body that resembles that of a female, but can be found with sperm in the ovaries, with a small number of eggs also being formed.

This means that even though the entire environment around the germ cells is female, functional sperm are created, which was surprising to scientists.

That means that this foxl3 gene acts as a sexual switch in germ cells that is completely independent of the body’s sex, an “entirely new finding,” Nishimura said according to the report.

While scientists have always known that germ cells can become either sperm or eggs, they didn’t know that there was a switch mechanism that determine which it would be.

The findings are of huge significance, as it helps scientists understand the mechanism behind sexual identity in vertebrates and reproduction itself.

The findings will be published in the journal Science, according to the report.