Scientists now understand how the single-celled organism called Tetrahymena thermophila mates. Over 50 years ago, scientists discovered that the organism has seven sexes. What remained unclear was how each cell's "mating type" or sex was determined.
Biologists from UC Santa Barbara, along with researchers from the Institute of Hydrobiology of the Chinese Academy of Sciences, and also the J. Craig Venter Institute, are responsible for the discovery.
According to the study, finding the genes that were possibly involved in mating required starving the cells which is a step required before conjugation (sex).
The team of researchers not only identified the mystery of the mating type gene, but they found the required DNA rearrangements for determining the sex. They describe this as "cut and paste" genomic recombination events. When this happens, all other gene pairs are deleted when one complete gene pair is assembled. Randomly, the sex is determined, similar to a roulette wheel.
"We found a pair of genes that have a specific sequence which is different for each mating type. They are very similar genes-clearly related to one another, going back probably to a common ancestor-but they have become different. And each is different in a specific way that determines the mating type of the cell,"
It was found that the genetic material located in the nucleus to be passed onto the offspring had gene pairs that were incomplete and there was one for each mating type. The Tetrahymena used in the study had just six sexes instead of seven. When DNA segments were fused to one of the six incomplete gene pairs, the other five were deleted. This left one pair and one mating type.
"The mating type of the 'parents' has no influence whatsoever on the sex of the progeny (offspring). It's completely random, as if they had roulette wheel with six numbers and wherever the marble ends up is what they get. By chance they may have same mating type as the parents-but it's only by chance. It's a fascinating system," said Eduardo Orias, a research professor emeritus and part of the UCSB team.
The updated findings about the multi-sexed, single-celled organism were published on March 26 in the PLOS Biology journal.
