Seven-gendered creature picks its sex at random

This single-celled creature has a lot when it comes to choice of sex —all seven of them!— and selects its gender using the genetic equivalent of a roulette wheel.

 

Meet the Tetrahymena thermophila, an oval-shaped protozoan that can choose its biological mating type by molecular chance, according to a report on LiveScience.com.

 

While scientists had been aware of Tetrahymena's seven sexes for 60 years, it is only now that they found how they select their sex.

 

"Finally, we had the resources to get at the molecular basis of it ― to actually discover the mating-type genes, what their sequence is, and how it is that the cells have the potential for many mating types and only end up expressing one ― a random one," study researcher and University of California, Santa Barbara biologist Eduardo Orias told LiveScience.

 

"We had no idea what a beautifully organized system this turned out to be. It's very modularly organized and very symmetrical in some ways and very ― to us ― aesthetically exciting," he added.

 

With seven instead of two sexes, it is easier for Tetrahymena meet a cell they can reproduce with, he noted.

 

Orias and his colleagues released their findings in the journal PLOS Biology.

 

The microscopic organisms live in freshwater and can mate with any other mating type except its own - and their offspring can have any one of the seven sexes.

'Cellular roulette'

 

Researchers looking into the Tetrahymena genome found what they described as the equivalent of a cellular roulette wheel.

 

The organisms have two nuclei each: the somatic nucleus contains the DNA while the germline nucleus acts like the cells in the ovaries or testes of humans.

 

"The DNA in the germline passes along traits to offspring," LiveScience said.

 

When two Tetrahymena fuse in their version of single-cell sex, they produce a gamete nucleus, the equivalent of a fertilized egg in humans.

 

The fertilization nucleus makes copies of itself, some of which are destined to become germline nuclei and some of which are somatic.

 

Researchers said it is here that the mating type is chosen: each germline nucleus has incomplete gene pairs, one for each of the organism's seven sexes.

 

"The cell joins and completes one of these gene pairs randomly, thus setting the cell's mating type. The rest of the incomplete gene pairs are thrown out," LiveScience said, quoting the report. — TJD, GMA News