In 1951 cells taken from an African American woman suffering from cancer were found to be unique because they carried on reproducing endlessly in the laboratory. Henrietta Lacks died of cervical cancer in 1951. Cultures from her cells have since been used to provide medical breakthroughs but as Farhana Haider reports, Henrietta Lacks was never asked if her cells could be used in medical research.

(Photo: Henrietta Lacks. Copyright: Lacks Family)

The epic mini-series about slavery in the USA hit TV screens in January 1977. Based on a novel by Alex Haley it imagined the lives of his ancestors who had been brought to the US from Africa on slave ships. It revolutionised perceptions about African-Americans and their history. Ashley Byrne has spoken to Leslie Uggams who played the character Kizzy in the series.

(Photo: Actors LeVar Burton, Todd Bridges and Robert Reed in Roots. Credit: Alamy)

In December 1976 unidentified gunmen tried to kill Bob Marley at his home in Kingston, Jamaica. The legendary reggae singer miraculously survived with just light injuries. Mike Lanchin has been hearing from Nancy Burke, one of Marley's friends and neighbours, who was trapped inside the house as the gunmen stormed in, guns blazing.

Photo: Bob Marley, 1970s (Michael Ochs Archives/Getty Images)

In November 1950, Clarence Adams, an African-American soldier fighting in the Korean war, was captured by the Chinese Red Army. He was held in a prisoner of war camp until the war ended. But instead of returning home, Adams and 20 other GIs chose to settle in China. Rob Walker has been speaking to his daughter, Della Adams.

(Photo: Clarence Adams and his Chinese wife, Liu Lin Feng, courtesy of the family)

Just three days after the 9/11 attacks on America, Congress gave the President the power to order military action against any person, organisation or country suspected of involvement in the attacks - without needing Congressional approval.

Witness speaks to Congresswoman Barbara Lee, the only member of the legislature to oppose the new powers.

Photo: Barbara Lee in 2002. Credit: Getty Images News.

In August 1969, Arthur Mitchell founded the Dance Theatre of Harlem - the first classical ballet company to focus on black dancers. Virginia Johnson, now the organisation's director, was a founder member.

(Photo: The Dance Theatre of Harlem, circa 1970. Virginia Johnson pictured back row, third from left. Credit: Marbeth)

In July 1981 race riots broke out on the streets of Liverpool. It was the first time that British police used CS gas to control civil unrest in mainland Britain. Witness has been hearing from a man who took part in the riot.

(Photo: Lines of police with riot shields face a group of youths during riots in the Toxteth area of Liverpool, July 1981. Credit: Keystone/Hulton Archive/Getty Images)

Robert Robinson, a Jamaican born engineer, was recruited to work in the USSR from a factory in Detroit in 1930. Having had his US citizenship revoked, he spent 43 years unable to leave the Soviet Union. Dina Newman tells his story, using BBC archive.

(Photo: Robert Robinson in the 1920s. Source: BBC archive)

In 1916 Marcus Garvey arrived in the US and began a movement for black pride. His dream was that black people would live independently of whites in a new empire in Africa.

Photo: August 1922 Marcus Garvey is shown in a military uniform as the "Provisional President of Africa" during a parade on the opening day of the Convention of the Negro Peoples of the World in Harlem, New York City. (Credit: AP Photo/File)

In April 1966, Ethiopia's emperor Haile Selassie made a spectacular arrival in Jamaica. It was his first and only visit to the birthplace of the Rastafarian movement which revered him. A quarter of a million people greeted him at the airport.

(Photo: Emperor Haile Selassie speaking to the BBC in 1954)

At the end of the 19th Century, African-Americans in the southern states of the US faced a wave of political and racial violence. Lynchings reached a peak. Black people were prevented from voting and subject to laws which enforced racial segregation.

In response, thousands sought to leave the US and travel to Liberia. More emigrants left from Arkansas than any other southern state.

We hear from Professor Kenneth Barnes of the University of Central Arkansas. He uncovered a fascinating series of letters that reveal why so many black Arkansans dreamed of Liberia and what happened to them when they got there.

(Photo: Departure of African American emigrants for Liberia; from The Illustrated American, 21 March 1896. Credit: The New York Public Library Digital Collections, 1890 - 1899)

In June 1980, the Guyanese opposition leader and academic, Dr Walter Rodney, was killed in a bomb explosion. He was one of the leaders of a movement trying to bridge the racial divide in Guyana’s politics. His supporters said he had been assassinated on the orders of the government. We hear from his widow, Patricia Rodney, and from Wazir Mohamed who was a young activist at the time.

(Photo: Walter Rodney. Credit: the Walter Rodney Family)

In 1931, nine black teenagers were convicted of raping two white girls in the southern US state of Alabama.

Eight were sentenced to death by an all-white jury; but after years of campaigning, all eventually went free.

We hear from the daughter of Clarence Norris, one of the accused.

Picture: Police escort two recently freed "Scottsboro Boys" New York, 1937, Credit: Associated Press

In 1925 a young black American dancer became an overnight sensation in Paris. Her overtly sexual act soon made her one of the most famous women in Europe. Her name was Josephine Baker - hear from her adopted son Jean-Claude Baker about her dancing, and her life.

(Photo: Josephine Baker in her heyday. Credit: Walery/Getty Images)

Birmingham in Alabama was one of the most segregated cities in the USA in 1963. In May that year thousands of black schoolchildren responded to a call from Martin Luther King to protest against segregation at the height of racial tensions. It became known as the Children's Crusade.

Gwendolyn Webb was 14 years old at the time and took part. Listen to her story.

(Photo: Firefighters turn their hoses on civil rights demonstrators in Birmingham, Alabama. Credit: AP Photo/Bill Hudson)

In 1958, a mixed-race couple, Mildred and Richard Loving, were arrested and then banished from the US state of Virginia for breaking its laws against inter-racial marriage.

Nine years later, Mildred and Richard Loving won a ruling at the Supreme Court declaring this sort of legislation unconstitutional.

Witness speaks to the Lovings' lawyer, Bernie Cohen.

Image: Mildred and Richard Loving, pictured in 1967 (Credit: Bettmann/Getty Images)

On 1 February 1960, four young black men began a protest in Greensboro, North Carolina against the racial segregation of shops and restaurants in the US southern states.

The men, who became known as the Greensboro Four, asked to be served at a lunch counter in Woolworths. When they were refused service they stayed until closing time. And went back the next day, and the next. Over the following days and months, this non-violent form of protest spread and many more people staged sit-ins at shops and restaurants.

Witness hears from one of the four men, Franklin McCain.

The Freedom Riders were civil rights activists who rode on buses, testing out whether bus stations were complying with the Supreme Court ruling that banned segregation.

Listen to Bernard Lafayette Junior, an eyewitness to how Martin Luther King managed to prevent inter-ethnic bloodshed on a night of extreme tension during the battle against segregation in the American South.

Picture: A group of Black Americans get off the 'Freedom Bus' at Jackson, Mississippi, Credit: William Lovelace/Express/Getty Images

Andrew Goodman was one of the three civil rights workers killed by the Klu Klux Klan in Mississippi in 1964. He and the other two victims, James Chaney and Michael Schwerner, had been working on a project to register African-Americans to vote.

For Witness, Andrew's brother David recalls his brother's strong sense of justice and what his family lived through in the 44 days he was missing. He remembers how nationwide shock helped change America for good - and that it took the deaths of two white people to awake the conscience of middle America.

Picture: Andrew Goodman, Credit: Associated Press

In 1968, when Petula Clark touched Harry Belafonte's arm during a duet, it was the first time a white woman had touched a black man on US television.

The sponsor insisted it be cut from the programme, but the programme makers refused.

Louise Hidalgo speaks to the producer of the programme, Steve Binder.

(Photo: Harry Belafonte. Credit: Alan Meek/Express/Getty Images)