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Female Fish Genetically Modified to Produce Sperm with Help from Scientists

Seriously Fish

Scientists genetically altered female rice fish to be able to produce usable sperm.

A team of researchers at the National Institute for Basic Biology in Japan have found a way to alter a single gene in female rice fish to allow them to create sperm instead of eggs.

A specific gene, foxI3, in the fish acts as a genetic switch that determines if germ cells are to become eggs or sperm. The sperm produced within the female ovaries is fully functional and capable of fertilizing eggs that can then hatch.

“While germ cells can become either sperm or eggs, nobody knew that in vertebrates the germ cells have a switch mechanism to decide their own sperm or egg fate,” Professor Minoru Tanaka told “Science.”

“Our result indicates that once the decision is made the germ cells have the ability to go all the way to the end. I believe it is of very large significance that this mechanism has been found.”

Only two female rice fish were originally created without the foxI3 embryos and that is when they discovered they started producing sperm within one week after hatching from their eggs.

These mutant fish also began to reproduce weeks earlier than normal males in the species. They went on to fertilize over half of the regular female’s eggs, almost all of which hatched.

Besides producing sperm instead of eggs, the genetically-modified fish looked and acted completely normal. They withheld their female body shape and continued to develop ovaries. The fish even continued to create sperm cells after more female hormones kicked in.

Mammals share a similar gene called foxI2 that triggers ovary development. This research is still too early to determine if the same results would be possible with a mammal’s much more complex reproduction system.


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Female Fish Genetically Modified to Produce Sperm with Help from Scientists