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The Tetrahymena thermophila is an organism that has seven different genders. The discovery was made over half a century ago, but it was not until recently that scientists discovered how the gender of their progenies was determined. After analyzing the organism's genetic makeup, researchers concluded that the gender of the organisms' offspring is decided based on a game like roulette.

The research team first observed the behaviors of multi-sex organisms and their reproductive systems. The researchers understood that these organisms reproduce based on a random genetic combination in which the offspring keeps only one pair of the genetic makeup and deletes the other from the parent. After analyzing the Tetrahymena, the researchers noted that the organism has two nuclei and one germiline. The germiline is where the genetic composition for the offspring can be found. It is in the germiline nucleus where incomplete gene-pairs are located and assigned randomly to determine the sex of the progeny.

"We found a pair of genes that have a specific sequence which is different for each mating," Eduardo Orias said. Orias is part of the UC Santa Barbara team of biologists who worked with researchers from the Institute of Hydrobiology of the Chinese Academy of Sciences and the J. Craig Venter Institute. "The mating type of the 'parents' has no influence whatsoever on the sex of the progeny. It's completely random, as if they had a roulette wheel with six numbers and wherever the marble ends up is what they get. By chance they may have the same mating type as the parents - but it's only by chance. It's a fascinating system."

The discovery that this multi-sex organism reproduces gender randomly provides insight into how this organism might be used in cancer research.

"By understanding this process better in Tetrahymena, what we learn ultimately may be of use in medicine. Tetrahymena has about as many genes as the human genome. For thousands of those genes you can recognize the sequence similarity to corresponding genes in the human genome with same biological function. That's what makes it a valuable organism to investigate important biological questions"

The findings were published in PLoS Biology.