A letter scientist Francis Crick wrote to his son about his Nobel Prize-winning DNA discovery has been sold to an anonymous buyer at a New York City auction for a record-breaking price of more than $6 million.

Elizabeth Van Bergen, a spokeswoman for Christie's auction house in New York, said the sale on Wednesday set a world auction record for a letter of $6,059,750.

The price eclipsed that for a letter from former US president Abraham Lincoln, which sold in April 2008 for $3.4 million.

On Thursday, the molecular biologist's 1962 Nobel Prize medal in physiology or medicine was scheduled to be offered by Heritage Auctions, which estimates it could fetch more than $500,000.

The items are among a dozen artifacts Crick's heirs are selling to benefit scientific research.

In the March 19, 1953, handwritten letter to his 12-year-old son, Michael, Crick describes his discovery of the structure of DNA as something "beautiful". The note tells his son how he and James Watson found the copying mechanism "by which life comes from life". It includes a simple sketch of DNA's double helix structure, which Crick concedes he can't draw very well.

The seven-page letter, written to his son in boarding school, concludes, "Read this carefully so that you will understand it. When you come home we will show you the model. Lots of love, Daddy".

Crick, 88, who died in 2004, was awarded the Nobel Prize along with Watson and Maurice Wilkins. He spent the latter decades of his career doing brain research at the Salk Institute, where he became a professor in 1977.

Michael Crick's daughter Kindra said the family decided to sell the medal and other items because they had been in storage for 50 years, first locked up in a room of her grandfather's home in La Jolla, California, and later in a safe deposit box.

They chose to sell them now because it "coincides with the 60th anniversary of the historic discovery and 50 years since he received the award", she said.

AP -AFP