The images of Algerian boxer Iman Helif and Taiwanese Lin Yu Ting on the podium in Paris will be some of the most unforgettable from the 2024 Olympic Games.
A heated debate has erupted over the International Olympic Committee (IOC) allowing them to compete in the women's competition in Paris, despite being disqualified from the Women's World Cup last year for failing to meet the criteria.
In the midst of this heated controversy, science is trying to explain the different structures of chromosomes and the advantages it can have in sports.
Research is ongoing, and even experts who work on it their entire professional lives have different interpretations.
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We know that the process of determining gender begins while the fetus is developing.
Most women get two X chromosomes (XX), while most men get an X and a Y chromosome (XY).
However, at some point during pregnancy, some babies' reproductive organs stop developing like most babies'.
This is known as a disorder of sexual development.
It includes a group of about 40 different states of genes, hormones and reproductive organs that develop in the womb.
This means that the sexual development of that person is different from that of most other people.
Chromosopathies are rare, but they came into the limelight due to a dispute over two female boxers at the Olympic Games.
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International Boxing Federation chief executive Chris Roberts told BBC Sport that XY chromosomes were found in "both cases".
However, it is not that simple.
There are many genetic variations and they are so different that some experts say it is impossible to determine that everyone with a Y chromosome is male and everyone without a Y chromosome is female.
"The mere presence of a Y chromosome does not answer the question of whether someone is male or female," explains Allen Williams, who researches how genetic factors influence sports performance at the University of Manchester's Institute of Sport in England.
"It's obviously a very good indicator, since most people who have a Y chromosome are men ... but it's not a perfect indicator."
In some people who have a disorder of sexual development, the Y chromosome is not fully formed, the typical male Y chromosome.
It may be missing some genetic material, it may be damaged or replaced by an X chromosome, depending on which variation it is.
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In terms of who is male or female, usually the part of the Y chromosome that contains a specific gene for developing testes (testis-determining factor (TDF)) is crucial.
"It's what's called a male-determining gene," says Emma Hilton, a biologist who studies genetic disorders.
She is also a representative of a charity organization Sex Matters which claims that Iman Helif and Lin Yu Ting should not compete until further analysis is done.
She says, "It's a major switch for sexual development."
There are some people born with XY chromosomes who have lost what Hilton calls the "male-determining" gene.
"These people don't produce testosterone. They develop very typical female genitalia," says Hilton.
Therefore, the test that determines XY chromosomes does not give a complete picture.
In the case of Iman Helif and Lin Ju Ting, the International Boxing Federation did not disclose details of how they were tested.
However, Hilton says that most people with XY chromosomes have a "male-determining" gene for testicular development.
"These people have testicles, often inside the body, and when they hit puberty, they start producing testosterone, which is what gives men an advantage in sports."
The most famous example is Caster Semenja - winner of two Olympic gold medals and three-time world champion at 800 meters.
The obstacle is in a gene needed for the development of the external genitalia - which boys need to grow a penis.
People like Kaster Semenje lack that gene.
In the womb, they develop the male sex organs until the final stage of penis growth - and when they are unable to do so, they begin to develop the pubis (vulva) and the clitoris.
But they don't develop female reproductive organs: they don't have a cervix or a uterus.
Such people do not menstruate and cannot conceive.
Sex with men can be difficult.
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Finding out that you have this type of genetic mutation can be shocking.
"The last woman we diagnosed with XY chromosomes was 33 years old," says Klaus Hojbjerg Gravholt, a professor of endocrinology at Aarhus University in Denmark, who has been dealing with disorders of sexual development for 30 years.
His patient approached him because she didn't know why she couldn't get pregnant.
"We discovered that she doesn't have a uterus, so she will never be able to have a baby."
"She was completely desperate."
Gravholt says the consequences of gender identity testing can be distressing, and she often refers patients to psychologists.
"If I showed you her photo, you would say: that's a woman.
"She has the body of a woman, she is married to a man.
"She feels like a woman. And so it is with most of my patients".
When Gravholt asked her why she didn't see a doctor because she wasn't getting her period, she said that there was an older woman in her family who never had a period, so she didn't think it was abnormal.
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There is another genetic mutation discovered by Gravholt.
He diagnosed men with XX chromosomes - which are usually found in women.
"These men are infertile.
"They look like normal men, but their testicles are smaller than average and they don't produce sperm.
"When they find out, they are always completely desperate.
"As they get older, they stop producing testosterone the way most men do."
In some societies, it is not acceptable to talk openly about menstruation and female genitalia.
In some parts of the world, women may not be educated enough to understand that something atypical is happening in their bodies.
And that's why experts believe that many people are never diagnosed with sexual development disorder - which means data is scarce.
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Do people who have a disorder of sexual development have an unfair advantage in sports?
The short answer is that there is not enough data to draw a definitive conclusion.
"It wouldn't surprise me if some people who have a disorder of sexual development have some physical advantage over women," says Allen Williams.
Some of these advantages are greater muscle mass, as well as larger and longer bones.
He believes that his opinion reflects the opinion of experts in his field, but that more evidence is needed.
In the cases of Iman Helif and Lin Ju Tiing, we do not have enough data to know whether they have a disorder of sexual development that should be regulated.
Introducing rules for elite sports, which usually rely on binary categories for competitions - male and female, is complicated because the biology itself is gender complex and not exclusively binary.
Some are calling for mandatory gender testing at the next Olympics, among them Rim Alsalem, the United Nations (UN) special rapporteur on violence against women and girls.
"DNA analysis is a cat's cough these days," says Emma Hilton.
"It is enough to take an oral swab and it is minimally invasive".
But there is disagreement among scientists about this.
"An oral swab doesn't allow you to make a firm conclusion about someone's gender and potential advantage in sports," says Dr. Allen Williams.
He claims that the gender test should include the following:
- Genetics (including looking for the Y chromosome and the "male-determining" testicle development gene)
- Hormones (including but not limited to testosterone)
- Mechanism of action of hormones such as testosterone. Some people may have a Y chromosome but be completely insensitive to testosterone.
He says that these tests are not currently performed because they are expensive and require the involvement of experts in very specific fields, and there are also ethical issues related to the testing process.
"Such an assessment can be humiliating.
"It includes measurements of the most intimate parts of the body, such as the size of the breasts and clitoris, the depth of the voice, body hair".
One thing is certain: this debate will not stop.
For now, science is not yet able to offer a definitive opinion on how people with a different chromosomal structure should be categorized in top sport.
Those who have spent their lives working to offer reasonable, science-based explanations hope this latest dispute will spark much-needed research.
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