No defined cellular pathway has ever been found for the development of the cells that define male and female in any form of life no matter how simple until now. A team of scientists led by Dr. James Umen with the Enterprise Institute for Renewable Fuels at the Danforth Plant Science Center are the first to find the gene that determines what sex an individual will become. The research was published in the July 8, 2014, edition of the journal Public Library of Science Biology.
The researchers studied two related species of multicellular green algae. Volvox carteri has two distinct sexes but can reproduce asexually. Chlamydomonas reinhardtii does not have two distinct sexes that can be defined by gametes. The scientists found that a single gene was responsible for the development of male and female gametes in Volvox carteri. The gene is called the Minus-Dominance Gene (MID).
The sperm cells of male Volvox carteri were found to be capable of being transformed into egg cells by inactivation of the RNA interference (RNAi) gene. Forcing female Volvox carteri to express the MID gene produced a conversion of egg cells into sperm cells. The altered male and female algae were capable of mating and producing viable offspring. MID from Chlamydomonas reinhardtii did not produce the sex change.
The conclusion is that at some point in time the MID gene developed a capability to differentiate sex in simple life forms. The researchers postulate that the MID gene may have been transferred to more complex life forms or more complex life forms evolved the MID gene independently. This is the first known discovery of a gene that determines the sex of an organism.
The research also demonstrates that the two primary forms of reproduction in plants and animals have a common origin. Both sexual and asexual algae in the study had the MID gene. The assumption is that a small chemical change produced the gene that determines sex in all plants and animals that exhibit sexual differences as male and female. The algae in the study are relatively young in terms of time. This indicates the differentiation of plants and then animals into different sexes was a relatively new modification in terms of time.