Rules requiring all athletes in the female category of world ranking events to take a one-time gene test come into force this week.
World Athletics says the sex screening – which detects the presence of a Y chromosome – is to protect the integrity of women’s competition.
But how does the latest attempt to tackle one of sport’s most contentious issues work? How did we get here, are there concerns, and what are the implications for the debate around gender eligibility? BBC Sport answers the key questions.
The test detects the SRY gene – or ‘sex-determining region Y gene’ – which is part of the Y chromosome and causes male characteristics to develop.
If a human embryo has XY chromosomes the SRY gene leads to the formation of testes, which then produce hormones including testosterone that lead to male development – increasing muscle mass and strength.
Research has shown athletes who were born male and passed through male puberty have physiological advantages over those born female (with XX chromosomes and no SRY gene).
The test is designed to determine biological sex in cases of athletes who are DSD – those born with ‘differences in sex development’. This is a term for a group of rare conditions, whereby a person’s hormones, genes and/or reproductive organs may be a mix of male and female characteristics. Some can be born with external female genitalia but functioning testes, and are often certified as female at birth and raised as such.
It is a cheek swab or blood test, which is done once in an athlete’s life by each national federation. If the test is negative for the Y chromosome – ie it is absent – the athlete is eligible to compete in the female category.