Organism with Seven Sexes Picks Gender Randomly

Researchers found half-a-century back that Tetrahymena thermophila has seven sexes, but it's only now that researchers have been able to find how these single-celled organisms find their mate.

The study team found that the sex of progeny in the case of multi-sex organism is determined randomly by genetic recombination that keeps one gene pair but deletes the others.

"We found a pair of genes that have a specific sequence which is different for each mating type," said Eduardo Orias, a research professor emeritus and part of a UC Santa Barbara team.

Each Tetrahymena has two nuclei, one germiline where the genetic information for the progeny is stored and the other somatic nuclei.

The germiline nucleus has similar but incomplete gene-pairs. Researchers describe the selection of the sex of the progeny as a game of roulette.

"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," Orias said in a press release.

The study has many applications in the field of cancer and organ transplant and in allorecognition, which is a tissue's ability to recognize itself from a foreign tissue.

"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," Orias said.

The study is published in the journal PLOS Biology.