Nobel Prize-winning American scientist James Watson, one of the co-discoverers of the structure of DNA, has died aged 97.

In one of the greatest breakthroughs of the 20th Century, he identified the double-helix structure of DNA in 1953 alongside British scientist Francis Crick, setting the stage for rapid advances in molecular biology.

But Watson's reputation and standing were badly hurt by his comments on race and sex. In a TV programme, he made claims about genes causing a difference in average IQ between black and white people.

His death was confirmed by Cold Spring Harbor Laboratory, where he worked and researched for decades, before having to resign as its chancellor over the comments.

Watson shared the Nobel in 1962 with Maurice Wilkins and Francis Crick for the DNA's double helix structure discovery.

"We have discovered the secret of life," they said at the time.

By the early 2000s, he had been largely ostracised by the scientific community over his comments on race and gender.

In 2007, the scientist told the Times newspaper that he was "inherently gloomy about the prospect of Africa", because "all our social policies are based on the fact that their intelligence is the same as ours - whereas all the testing says not really".

He apologised "unreservedly", but nevertheless, the comments led to him losing his job as chancellor at Cold Spring Harbor Laboratory in New York.

Additional comments he made in 2019 - when he once again suggested a link between race and intelligence - led to the lab stripping his honorary titles of chancellor emeritus, Oliver R Grace professor emeritus and honorary trustee.

"Dr Watson's statements are reprehensible, unsupported by science," the laboratory said in a statement at the time.

DNA was discovered in 1869 but it took until 1943 for scientists to discover that it made up the genetic material in cells. Still, the structure of DNA remained a mystery.

Working with images obtained by King's College researcher Rosalind Franklin, without her knowledge, Crick and Watson were able to construct a physical model of the molecule.

Maurice Wilkins, who shared the Nobel with Crick and Watson, had worked with Franklin to determine the DNA molecule's structure. Franklin, who died in 1958, is today recognised for the integral role she played in the scientific breakthrough of DNA research, despite her work largely being written out of the story at the time.

Former colleagues have commented that Watson nurtured the careers of female scientists at Harvard in the 1950s and 60s, at a time when that was not the norm. However he also made disparaging comments about women in science, and wrote sexist remarks about Franklin, including commenting on her appearance, in his 1968 best-selling book, The Double Helix.

Watson became the first living Nobel laureate to sell his gold medal, fetching $4.8m (?3.6m) at an auction in 2014, saying he was letting go of it because he felt ostracised by the scientific community after his controversial remarks.

A Russian billionaire bought it for $4.8m and promptly gave it back to him.

James Watson was born in Chicago in April 1928 to Jean and James, descendants of English, Scottish and Irish settlers.

He won a scholarship to study at the University of Chicago at the age of 15.

There, he became interested in the new technique of diffraction, in which X-rays were bounced off atoms to reveal their inner structures.

To pursue his research into DNA structures, he went to Cambridge University in England, where he met Crick, with whom he began constructing large-scale models of possible structures.

Later, after his scientific discovery, Watson and his wife, Elizabeth, moved to Harvard, where he became professor of biology. The couple had two sons - one of whom was diagnosed with schizophrenia as a teenager, further motivating Watson's research to learn more about DNA in the hope of possibly helping him.

In 1968, he took over the Cold Spring Harbor Laboratory in New York State - an old institution which he was credited with turning into one of the world's foremost scientific research institutes. (BBC)

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