A single gene is sometimes all it takes to change a slime mold's sexual identity.

The social amoeba Dictyostelium discoideum has three different sexes — members of one sex, or 'mating type', can fuse with either of the other two to form giant, dormant cysts. But little is known about what genes determine the sexual identity of a slime mold.

Gareth Bloomfield of the Medical Research Council molecular biology lab in Cambridge, UK, and his colleagues found a region of the D. discoideum genome that differed among sexes. Deleting a gene from this region prevented mating-type I from coupling with mating-type II; reintroducing the gene restored normal sexual orientation. Meanwhile, swapping sex genes from one mating type to another caused the amoebae to switch sexual partners.

Science 330, 1533–1536 (2010)