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More than just X and Y: New genetic basis for sex determination
The team found that miRNAs are essential for sex determination even after an animal has grown to adulthood. "They send signals that allow germ cells, i.e., eggs and sperm, to develop, ensuring fertility," Fagegaltier explains. "Removing one miRNA from mature, adult flies causes infertility." More than that, these flies begin to produce both male and female sex-determinants. "In a sense, once they have lost this miRNA, the flies become male and female at the same time," according to Fagegaltier. "It is amazing that the very smallest genes can have such a big effect on sexual identity."
Some miRNAs examined in the study, such as let-7, have been preserved by evolution because of their utility; humans and many other animals carry versions of them. "This is probably just the tip of the iceberg," says Fagegaltier. "There are likely many more miRNAs regulating sexual identity at the cellular and tissue level, but we still have a lot to learn about these differences in humans, and how they could contribute to developmental defects and disease."