Scientists said they caused female mouse embryos to develop into males by injecting a gene, providing new evidence that the gene is the "sex trigger" that determines gender.

The gene, injected into fertilized mouse eggs, produced two embryos that had normal male sex organs and a mouse that showed normal male mating behavior.The gene appears to work by regulating the activity of other genes. Previous studies had also implicated it and its counterpart in humans in the process of determining sex.

Although the research is in its early stages, agricultural companies have already asked about manipulating the sex of farm animals, study co-author Robin Lovell-Badge of the Medical Research Council National Institute for Medical Research in London said in a telephone interview.

Lovell-Badge said he expected no application in human reproduction, and another scientist, commenting on the research Wednesday, said the process by which gender is determined in humans appears to be more complicated.

Lovell-Badge and colleagues at the institute and the Imperial Cancer Research Fund in London presented the work in Thursday's issue of the British journal Nature.

"I think this is a pretty dramatic demonstration that this is the sex-determining gene on the Y (chromosome), at least in the mouse," commented Dr. David Page of the Howard Hughes Medical Institute at the Whitehead Institute in Cambridge, Mass. But there may be more to the story in people, Page said.

In mammals, embryos develop as females unless they contain the Y chromosome. A chromosome is a string-like collection of genes. Scientists have been trying to discover what gene or genes on the Y chromosome trigger the process of making a male.

The key event is the creation of testes rather than ovaries from a particular bit of tissue in the embryo, researchers said in Nature.


(Additional information)

Gene holds key to sex determination

Scientists in London have found that a particular gene, called Sry, is a "sex trigger" that determines the gender of developing mouse embryos. The discovery was made by injecting the gene into fertilized egg cells. The gene made the female embryos develop into male mice.

What is a gene?

Genes hold information for all aspects of bodily growth and development. They are segments of DNA within chromosomes. DNA (deoxyribonucleic acid)is a series of long molecules that contain coded instructions.

Find the "sex trigger" in chromosomes

A normal human chromosome set is 22 pairs plus one pair of sex chromosomes called X or Y. Mammals develop as females unless they contain the Y chromosome.

Scientists have discovered that a gene called Sry in the Y chromosome triggers the process of determining a male in mice. Even mice that did not have a Y chromosome became male if they were injected with the Sry gene, but those mice were sterile.

Female has two X chromosomes

Male has one X and one Y chromosome

Source: The AMA Home Medical Encyclopedia