New Biological Insight: The Gender of Fresh-Water Organism is Determined Randomly

Over 50 years ago, an organism was discovered that has seven different genders that can mate in 21 different ways.

Today, scientists say they've discovered the genders of offspring of that multi-sex creature, the fresh-water Tetrahymena thermophile, is determined randomly. That, they say, gives them a better understanding how all cells --- like those leading to cancer --- work.

After analyzing the organism's genetic makeup, scientists found the gender of the organisms' progeny is decided much like a game of chance, like roulette.

"We found a pair of genes that have a specific sequence which is different for each mating," said Eduardo Orias, a scientist from the University of California Santa Barbara who worked alongside 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...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," he said.

After observing the behaviors of the multi-sex organisms and their reproductive processes, the researchers realized the 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.

The research team found has two nuclei and one germiline, which is where the genetic composition for the offspring is formed. The germiline nucleus is where incomplete gene-pairs are located and combined randomly to determine the offspring sex.

"By understanding this process better in Tetrahymena, what we learn ultimately may be of use in medicine," Orias said. " 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 study was published in PLoS Biology.