Biology textbooks may need to be re-written, with scientists finding a new piece of DNA essential to forming male sex organs in mice.

An international research collaboration with The University of Queensland found the Y-chromosome gene that makes mice male is made up of two different DNA parts, not one, as scientists had previously assumed.

UQ’s Institute of Molecular Biosciences Emeritus Professor Peter Koopman said the critical DNA fragment had been hidden from researchers for more than 30 years.

«Expression of the Y chromosomal gene Sry is required for male development in mammals and since its discovery in 1990 has been considered a one-piece gene,» he said.

«Sry turns out to have a cryptic second part, which nobody suspected was there, that is essential for determining the sex of male mice. We have called the two-piece gene Sry-T.»

The scientists tested their theory and found that male mice (XY) lacking in Sry-T developed as female, while female mice (XX) carrying a Sry-T transgene developed as male.

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Materials provided by University of Queensland. Note: Content may be edited for style and length.