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Transgender algae help scientists crack mystery of evolutionary origin of male and female sexes

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Algae may provide researchers with information regarding the nature of gender for the first time.

A single gene determines whether some modern multicellular algae organisms are male or female. Biologists now believe that genetic aspect have evolved in a form of single-celled algae which does not present a specific gender. If this theory is confirmed by other researchers, it could reveal the genetic underpinnings of sexual reproduction.

Sex is a method of reproduction commonly found throughout plant and animal species. This form of reproduction first evolved between one billion and 500 million years in the past. Time and radical adaptations make it challenging to pinpoint the initial development of sex and gender.

"Single-cell organisms have sex, too. They do it when cells of two different mating types, but of the same species, fuse," James Umen, an evolutionary biologist at Washington University, said.

The ancient single celled Chlamydomonas reinhardtii reproduced asexually. Just a few hundred million years later, the multicellular Volvox carteri was divided into male and female organisms. On an evolutionary time scale, this adaptation occurred in a relatively short period.

The genetic code of each of these organisms contains a gene labeled MID. Within the more-primitive C. reinhardtii, MID is present in the "plus" mating type, but missing in the "minus" variety. A form of the gene is present in males of V. carteri, but absent from females. Researchers determined that the form of MID present in the multicellular organisms evolved from the earlier species.

Umen removed the gene from male members of V. carteri, and the cells responded by converting sperm packets into eggs. When MID was placed into the genetic code of females, reproductive organs morphed into male structures. By changing this single gene, researchers were able to easily change the sex of cells. This could act as a master switch controlling gender in similar organisms.

"By manipulating this one gene we can essentially give Volvox a sex change," Umen said.

Unlike the more developed organisms, C. reinhardtii does not have reproductive cells. The production of sperm and egg cells requires the presence of a more complex management system than simpler systems. This simple change may have been one of the early adaptations in species which led to sex. Followup research will attempt to understand how the gene came to control the mechanism of gender.

Investigation of gender assignment in algae was profiled in Plos One Biology.

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