FACTBOX - Key facts on gender testing

REUTERS - The rapid improvement of South African teenager Caster Semenya, who won the women's world 800 metres title, has prompted officials to order a gender verification test.

Here are some details about sex testing, which was introduced more than 40 years ago.

* CONDUCTING TESTS:

-- Laboratory and genetic testing were introduced at the 1968 Mexico City Olympics.

-- Women typically have two X chromosomes and men have an X and a Y chromosome in each of their cells. The presence of two X chromosomes is taken as confirmation of the athlete's female gender. Test results for about one in 500-600 athletes are abnormal.

* TESTING:

-- The International Association of Athletics Federations abandoned gender verification tests in the early 1990's concluding they were not needed. This was thought to be especially true because of the current use of urine testing to exclude doping: voiding is observed by an official in order to verify that a sample from a given athlete has actually come from his or her urethra.

-- The International Olympic Committee (IOC) suspended the tests before the 2000 Sydney Olympics. However, the Olympic Council of Asia still conducts tests.

* TRACK RECORD: