New York, Aug 19 (IANS): Not just the X and Y chromosome but a subset of very small genes also play a key role in differentiating male and female tissues in the fruit fly, researchers reported.

Called microRNAs (miRNAs), these are a short segment of RNA that fine-tunes the activation of one or several protein-coding genes.

miRNAs are able to silence the genes they target and, in doing so, orchestrate complex genetic programmes that are the basis of development.

"We found that the differences in miRNAs are important in shaping the structures that distinguish the two sexes. In fact, miRNAs regulate the very proteins that act as sex determinants during development," said Delphine Fagegaltier from Cold Spring Harbor Laboratory (CSHL) here.

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 (eggs and sperm) to develop ensuring fertility

"Removing one miRNA from mature adult flies causes infertility," Fagegaltier noted.

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. It is amazing that the very smallest genes can have such a big effect on sexual identity," Fagegaltier added.

The study appeared in the journal Genetics.