The discovery of the human chromosome number in Lund, 1955–1956
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The correct determination of the human diploid chromosome number as 46, by J-H Tjio and A Levan, at the University of Lund, Sweden, occurred 50 years ago, in December 1955; the finding was published in April 1956, ending a period of more than 30 years when the number had been thought to be 48. The background to the discovery and the surrounding factors are reassessed, as are the reasons why previous investigators persistently misidentified the precise number. The necessity for multiple technological advances, the power of previously accepted conclusions in influencing the interpretation of later results, and the importance of other work already undertaken in Lund, are all relevant factors for the occurrence of this discovery, the foundation for modern human cytogenetics, at this particular time and place.
This paper has its origins in a series of recorded interviews with early workers in human cytogenetics during 2003–2004, and from an invitation by the University and the Mendelian Society of Lund to give their 2004 Nilsson-Ehle lecture. I should like especially to thank all those workers in Lund for their kindness, hospitality and for generously sharing their information and memories, concerning this important period. However, any inaccuracies or misinterpretations are entirely my own responsibility. Special thanks are due to the following Lund workers: Professors Bengt O. Bengtsson, Arne Hagberg (former director of Svalöf Institute), Ulf Kristoffersson, Felix Mitelman, and Drs Eva and Yngve Melander. Outside Sweden I am particularly grateful to Professors David Harnden and Maj Hultén for sharing their memories of this time.
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