Sumida's team crossed two frogs with recessive genes through artificial insemination and the offspring looked normal due to the presence of more powerful genes. But crossing the offspring led to a frog whose skin is transparent from the tadpole stage.
"You can see dramatic changes of organs when tadpoles mutate into frogs," said Sumida, whose team is seeking a patent.
Such frogs could theoretically exist in the wild but it is "virtually impossible" they would naturally inherit so many recessive genes, Sumida said.
The transparent frogs can also reproduce, with their offspring inheriting their parents' traits, but their grandchildren die shortly after birth.
"As they have two sets of recessive genes, something wrong must kick in and kill them," Sumida said.
While the researchers relied on artificial insemination, they said that genetic engineering could also produce transparent and even illuminating frogs.
Sumida said researchers could also inject into the transparent frogs an illuminating protein attached to a gene, which would light up the gene once it manifests — for example, showing at what stage cancer starts.
Sumida said it would be unrealistic to apply the same method to mammals such as mice as their skin structure is different.
