What is DSD? The condition at the heart of the controversial Imane Khelif and Angela Carini Olympic boxing bout

OLYMPIC boxer Imane Khelif has sparked a row about sex in sport after being allowed to fight as a woman despite failing a 'gender test' last year.

The Algerian, 25, won her bout on Thursday after Italy's Angela Carini threw in the towel after less than a minute of being clobbered by her opponent.

Khelif has previously been disqualified from the world championships for failing to meet the biological requirements to fight as a woman.

It is not known exactly how she failed the test – but the furore has shone the light on conditions called differences in sex development, or DSD.

People with differences in sex development (DSD) have biological components of both sexes.

They are often more one sex than the other, which may determine how they live their life.

The Olympics said it uses the sex on someone's passport as proof of their category.

It is not known whether Khelif has a difference in sex development, and she has not commented on the situation.

On Friday, International Olympic Committee spokesman Mark Adams said: "The Algerian boxer was born female, was registered female, lived her life as a female, boxed as a female, has a female passport."

What is a difference in sex development?

Typically, men have XY chromosomes, high testosterone and a penis and testicles, while women have XX chromosomes, high oestrogen and a womb and vagina.

Someone with DSD, which may also be known as intersex, can have a mixture of these.

The cause is a genetic mutation before birth which goes on to affect the body's hormone levels and physical development.

There are many types of DSD and people may develop in a range of different ways, some more noticeable than others.

Some people may become an almost even split between male and female, with the hormones and body parts of both.

While others, such as women with Mayer-Rokitansky-Küster-Hauser (MRKH) Syndrome, may have almost totally normal female development but grow up without a womb.

Some people may not find out they have a DSD until adulthood, while others are diagnosed at birth.

Why is it an issue in sport?

It is a rare issue but has cropped up in sport when women with strong male characteristics have competed in female categories.

A woman with a DSD may have particularly high levels of testosterone, for example because they have developed testicles inside their body as well as female sex organs.

Extra testosterone can help them grow larger and more muscular than a typical woman, to be physically more like a man.

This may give them a competitive advantage in certain sports, particularly where power, body size, lung capacity or explosive strength are involved.

Testosterone is so good for building muscle that some bodybuilders take anabolic steroids to increase their levels of it.

Imane Khelif came under fire after her Italian opponent appeared to withdraw out of fear she would be seriously hurt by her much stronger rival.

A second boxer in the Olympics, Taiwan's Lin Yu-Ting, is also in the spotlight for continuing to fight despite failing a gender test last year.

A high-profile DSD case was of champion South African sprinter Caster Semenya, who was banned from competition and forced to take a sex verification test due to her high testosterone.

Her testosterone levels were higher than that allowed by female competitors but she lived her life as a woman.

Scientists say using testosterone levels alone is not an accurate way to differentiate between male and female because of natural variation, with levels usually high in strong athletes.

Is this the same as transgender athletes?

No, having a DSD is not the same as being transgender.

Someone with a DSD may identify as one sex while having strong characteristics of the other, but it is a natural biological mix.

A transgender person is usually born one sex and then lives as the other because they feel that is their true identity.

They can make biological changes with surgery, medicine or hormone drugs but they do not happen naturally.

Find out more about DSD from the .