Images of the Algerian boxer Imane Khelif and Taiwan’s Lin Yu-ting on the medal podium in Paris will go down as some of the most unforgettable of the 2024 Olympics.
A frenzied debate has raged over the International Olympic Committee clearing the duo to compete in the women’s boxing in Paris, despite them having been disqualified from last year’s Women’s World Championships for failing to meet eligibility criteria.
Amid the heat, science is shedding increasing light on our different chromosomal make-ups and what advantages they may bring to sport.
But the research is ongoing and even among the experts who spend their professional lives working on it, there are differing interpretations on what the science tells us.
We do know that the process of sex determination starts when a foetus is developing. Most females get two X chromosomes (XX), while most males get an X and a Y chromosome (XY).
Chromosomes influence a person’s sex. But hormones are important too, before birth – as well as later on during puberty. While the baby is still growing in the womb, hormones help the reproductive organs develop.
However, at some point through the pregnancy some babies’ reproductive organs don’t develop in the way most people’s do.
This is known as DSD: differences of sex development.
There are a group of about 40 conditions involving genes, hormones and reproductive organs that develop in the womb. It means a person’s sex development is different from that of most other people’s.
These chromosome abnormalities are rare – but they have come into sharp focus because of the boxing row at the Olympics.
So what do we know about the two boxers at the heart of the gender row?
The International Boxing Association chief executive Chris Roberts told BBC Sport that after both athletes had agreed to medical tests, XY chromosomes were found in “both cases”.
But it’s not that simple.
Because these genetic variations are so many and so varied, some experts say it’s impossible to establish that everyone with a Y chromosome is a male and everyone without a Y chromosome is a female.
“Just looking at the presence of a Y chromosome on its own does not answer the question of whether someone is male or female,” says Prof Alun Williams, who researches genetic factors related to sport performance at the Manchester Metropolitan University Institute of Sport.
“It’s obviously a very good marker, as most people with a Y chromosome are male…but it’s not a perfect indicator.”
For some people with DSD, the Y chromosome is not a fully formed typical male Y chromosome. It may have some genetic material missing, damaged or swapped with the X chromosome, depending on the variation.
When it comes to being male or female, what is usually crucial is a specific gene called SRY – which stands for ‘sex-determining region of the Y chromosome’.
“This is what is called the make-male gene. It’s the master switch of sex development,” says Dr Emma Hilton, a developmental biologist who studies genetic disorders. She is also a trustee of the Sex Matters charity, which argues Imane Khelif and Lin Yu-ting shouldn’t be competing until further testing is done.
