Gene tests begin in women's athletics - new rule explained

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 - and can increase muscle mass and strength.

Research has shown athletes who were born male and passed through male puberty generally 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.

However, World Athletics says that a positive test may occur if the athlete has the DSD condition 46 XY, and that "such individuals with typically male chromosomes may have atypical development of reproductive or sexual anatomy due to variations in the SRY gene or other related genetic factors", with some assigned a female gender at birth.

In such cases, unless the athlete has complete androgen insensitivity syndrome (CAIS) - and has not gone through male puberty - they would be ineligible to compete in the female category.

World Athletics is also allowing "a very small number of known DSD athletes to compete under the current regulations", as long as they continue to comply.

World Athletics says more than 90% of the athletes due to take part in the World Championships later this month have been tested, with any outstanding cases to be conducted in Tokyo.

Its president Lord Coe has admitted the time frame has been "tight", and that there has been "added complexity" because genetic testing for non-medical reasons is outlawed in some countries, such as France and Norway, so some athletes have had to give samples overseas.

A group of Canadian athletes also had to be retested after a reported 'test-tube error' meant their cheek swabs failed to comply with requirements.

Gender in sport has been a major issue since 2009, when South African Caster Semenya won the 800m final at the World Championships in Berlin - going on to dominate at the distance.

She was born with 46 XY 5-ARD (5-alpha-reductase deficiency). People with this particular DSD have male XY chromosomes, but some are recorded as female at birth.

Semenya was legally registered as female at birth and has said that although she was born without a uterus and with internal testicles, she has a vagina and is a woman.

At the 2016 Olympics in Rio, all three medallists in the women's 800m (including winner Semenya) were DSD athletes, intensifying calls for tighter rules. World Athletics then insisted that for track events from 400m up to the mile, DSD athletes must reduce their testosterone levels in order to be eligible.

Semenya refused, arguing it was an infringement of her human rights and discriminatory.

Amid a long legal battle, World Athletics' made its rules stricter in 2023. Transgender women who had gone through male puberty were banned from competing in women's events, while DSD athletes had to further reduce their testosterone levels and for longer, and in all track and field events.

Then, earlier this year, a World Athletics working group recommended going further still, claiming new research showed testosterone suppression could only partly mitigate the overall male advantage.

The governing body said the SRY gene is "a reliable proxy for determining biological sex" and that the majority of those it consulted supported a cheek swab test.

"It is really important in a sport that is permanently trying to attract more women that they enter a sport believing there is no biological glass ceiling," said Lord Coe at the time.

"At elite level, for you to compete in the female category you have to be biologically female."

World Boxing also introduced mandatory sex testing this year, with any fighters wanting to take part in the female competition at the World Championships in Liverpool this week having had to take a test.

"Athletes that are deemed to be male at birth, as evidenced by the presence of Y chromosome genetic material (the SRY gene) or with a difference of sexual development (DSD) where male androgenization occurs, will be eligible to compete in the male category," the governing body said in May.

This followed a major controversy in the women's boxing competition at the 2024 Paris Olympics, where Imane Khelif and Lin Yu-ting both won golds despite being disqualified from the previous year's World Championships for allegedly failing gender eligibility tests conducted by then governing body the IBA.

The IBA was then suspended and so the International Olympic Committee (IOC) ran the boxing competition in Paris and allowed the fighters to compete, insisting they met eligibility requirements. This sparked scrutiny over whether the body had put inclusion over fairness and safety, and the reliability of the IBA's original tests.

The IOC has been wary of sex screening for fear of stigmatising or discriminating against athletes. In 2024, then president Thomas Bach also said: "It is not as easy as some may now want to portray it - that XX or XY is the clear distinction between men and women. This is scientifically not true any more."

However, after the Paris 2024 boxing controversy, the United Nations' special rapporteur on violence against women called for sex screening for female athletes, external to be reintroduced. A group of 32 academics agreed,, external claiming it was "overwhelmingly preferable to targeted testing based on allegations, suspicion and bias".

New IOC president Kirsty Coventry says protecting the female category is a priority, and seems open to applying such a test across all sports. Meanwhile, US President Donald Trump has said sex testing in some form will be applied for women's competition at the LA Olympics in 2028.

However, Andrew Parsons, the president of the International Paralympic Committee, says he is opposed to "blanket solutions" to gender eligibility, suggesting each federation should still be left to decide its own rules.

The IOC used visual inspections in the 1960s, but there were concerns they were degrading and invasive, before mandatory chromosome-based cheek swab tests were introduced.

There were still issues, however. Spanish hurdler Maria Jose Martinez Patino was barred from competition in 1986 after failing the test, but later examinations showed that while she had XY chromosomes she also had CAIS - meaning her body never gained benefits from the increased testosterone created by her internal testes.

She was reinstated, but amid a number of 'false positives', and fears that female athletes were being punished for natural variations, gender verification tests were abolished in the 1990s.

World Athletics insists the new tests are now "extremely accurate and the risk of false negative or positive is extremely unlikely".

Lord Coe says athletes have been "overwhelmingly supportive" of the new tests. Campaign group Sex Matters said the return of screening was "welcome and overdue", adding: "Every sport needs to follow the lead of World Athletics and World Boxing."

However, US runner Nikki Hiltz - who is transgender and non-binary - said the gene testing was "disappointing", adding: "I just don't like the precedent that it sets."

Hiltz - who has qualified for the World Championships and has taken a test - expressed concern, external it might mean more invasive techniques are used, and that the estimated $100 (£74) cost for each test would be better spent tackling doping or abusive coaches.

Within the scientific community there is also opposition. Andrew Sinclair, a professor of translational genomics at the University of Melbourne - who discovered the SRY gene in 1990 - recently wrote that mandatory sex testing was "misguided"., external

He said that "using SRY to establish biological sex is wrong because all it tells you is whether or not the gene is present," and that "the science does not support this overly simplistic assertion". He also raised concerns about the risk of accidental contamination and a potential false positive.

And Madeleine Pape, a former Australian Olympian and a sociologist at the University of Lausanne, has also raised concerns about the test inadvertently 'outing' athletes - some of whom may never have known they had a DSD.

"It is far from being scientifically accurate as a performance indicator, while being very harmful to the athletes affected," she said.

World Athletics says any initial positive results will be followed up with further medical assessments, allowing for an accurate diagnosis before a decision over eligibility is made. It says a healthcare specialist will also discuss the results with an athlete, helping them understand any medical, psychological or social implications.

In terms of privacy, athletes have been told they will upload their test result on a secure, encrypted platform, and that they can request a retest and challenge results via the Court of Arbitration for Sport (CAS).

Supporters also say this method is more humane than requiring DSD athletes to suppress their natural testosterone levels, and will avoid the intense media scrutiny that some athletes have been subjected to.

Some experts are predicting legal challenges, although Lord Coe says he's confident the policy will stand up to any - insisting international human rights standards are being respected.

Semenya has waged a long legal battle against the previous sex eligibility rules. In 2019 she unsuccessfully challenged them at CAS. However, in July the European Court of Human Rights found her right to a fair hearing was violated by the Swiss Federal Supreme Court when she lost a further appeal in 2020.

That partial victory may mean renewed scrutiny on regulations that some sports say are needed to protect fairness in the female category, but which critics argue are unethical and discriminatory.