Differences in sex development (DSD) have become a central point of controversy at this year's Olympics after 'biological male' Algerian boxer Imane Khelif beat an opponent in the women's boxing event.

Khelif was banned from a previous women's tournament after failing a 'gender assessment' but was controversially given the greenlight to compete at this year's games. 

And facing off against Italy's Angela Carini, Khelif was victorious after just two blows with her opponent yelling 'this is unjust' as the match was abandoned.

Khelif hasn't yet commented on the subject but speculation abounds that she has a DSD, a rare condition that only affects between 0.05 and 1 percent per cent of the population. 

Also called 'intersex' conditions, DSDs can result in outwardly female individuals having male chromosomes or anatomy.

DSD is an umbrella term for 40-plus individual conditions which develop in the womb.

For example, a person can be born with female genitalia but have the XY chromosome combinate typical of males as well as internal hidden testicles. 

They can give people unusual combinations of chromosomes and reproductive organs, which in the context, of sport can boost their performance.

For example, an athlete may be born with female anatomy but have a DSD which boosts her level of testosterone, a hormone critical to building muscle and strength. 

While many DSDs are spotted at birth, some only come to light in puberty or as a result of a medical operations, test and even autopsies.  

In some cases, athletes have only learned they have a DSD during pre-competition medical tests, which have led to them being disqualified and ending their dreams of representing their country. 

One of the most famous examples of DSD in sport is that of South African runner Caster Semenya.

An Olympic gold medalist, Semenya has a DSD called 5-alpha-reductase deficiency, which means she has the male XY chromosomes and produces higher levels of testosterone than normal for women.

This DSD can occur in people with female reproductive anatomy and genitalia as in Semenya's case.

She has previously detailed how she has male, but internal, testes, and no uterus but does have a vagina. 

Semenya, who dominated women's running events between 2009 and 2019, learnt at the same time as the rest of the world that she had a DSD. 

She was controversially forced to take drugs like the contraceptive pill to lower her testosterone to align with new rules that limited the level of the hormone in women's events. 

Semenya has previously shared how this gave her 'panic attacks', caused her severe stress and made her 'want to throw up every day'.

The subject of her DSD, and if she was discriminated against by sporting bodies, have been the subject of an extended legal battle. 

And she's not the only athlete to be caught up in the storm. 

Fellow runners Francine Niyonsaba of Burundi, Kenya's Margaret Nyairera Wambui, and Namibia's Christine Mboma and Beatrice Masilingi have also been ruled ineligible to compete in competitions due to DSDs. 

While most people with DSDs live perfectly normal and healthy lives some conditions can be severe and require involved medical care. 

While some DSDs can run in families, in most cases what exactly triggers it occur during development in the womb is unknown. 

Worldwide, up to 1.7 per cent of people have intersex traits — roughly the same proportion of the population who have red hair — according to the Office of the United Nations High Commissioner for Human Rights.

The British charity DSD Families estimates that around 130 babies born in the UK each year need investigations for potential intersex conditions. 

Historically people with DSDs have sometimes been subjected to shocking medical treatment and still do so in some parts of the world. 

For example, so-called 'corrective surgeries' have been sometimes used to 'fix' babies' genitalia to better match one sex, without medical need. 

For example, male babies born without a penis, a DSD called aphallia, have sometimes been subjected to 'feminisation surgery' to create an artificial vagina.

But such surgeries only account for appearance of genitalia and not how a person's body is actually built. 

In the above example, this has resulted in people being raised as girls only to grow facial hair and a deeper voice when their male puberty starts which can cause them incredible distress. 

DSD charities have also criticised this 'corrective 'approach as it usually driven by societal expectations of what a person should look like rather than any medical benefit for the patient.

The subject of DSDs, and the potential advantage women with these conditions may have, has become a subject of controversy at this year's Olympics. 

At the centre of the storm is Khelif who was banned from a previous women's international competition event after tests reportedly found she had 'male sex chromosomes' leading to comments she is a 'biological male'. 

At the time International Boxing Associate president, Umar Kremlev, claimed the tests had proven Khelif 'had XY chromosomes', which are an indicator someone is male. 

He added that they 'uncovered athletes who were trying to fool their colleagues and pretend to be women'. 

However, and to great controversy, she was cleared to enter the Paris games.

In a shocking match today against Italy's Carini that only lasted 46 seconds Khelif dominated with the fight abandoned after she delivered two powerful blows.

Sports scientists have told MailOnline that pitting a 'biological male' against a female opponent was equivalent to pitting a 90kg fighter against a 60kg competitor. 

Khelif has yet to comment on speculation about her medical history, but has previously told Algerian media she has had high levels of the hormone testosterone since birth. 

But ahead of the fight the Algeria's Olympic Committee (COA) condemned what they called 'baseless' attacks on Khelif.

'COA strongly condemns the unethical targeting and maligning of our esteemed athlete, Imane Khelif, with baseless propaganda from certain foreign media outlets,' they said. 

'Such attacks on her personality and dignity are deeply unfair, especially as she prepares for the pinnacle of her career at the Olympics. The COA has taken all necessary measures to protect our champion.'