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The chromosome number in humans: a brief history


Following the rediscovery of Mendel's work in 1900, the field of genetics advanced rapidly. Human genetics, however, lagged behind; this was especially noticeable in cytogenetics, which was already a mature discipline in experimental forms in the 1950s. We did not know the correct human chromosome number in 1955, let alone were we able to detect a chromosomal abnormality. In 1956 a discovery was reported that markedly altered human cytogenetics and genetics. The following is an analysis of that discovery.

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Figure 1: Theophilus S. Painter
Figure 2: Camera lucida drawing of a human spermatogonial metaphase made by Theophilus S. Painter.
Figure 3: Albert Levan.
Figure 4: Joe Hin Tjio.
Figure 5: A human metaphase plate, from the original Tjio and Levan paper, showing 46 chromosomes.


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I thanks my colleagues, A. Motulsky and R.S. Hansen, for careful reading of the manuscript. The work in the author's laboratory is supported by a grant from the US National Institutes of Health.

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Gartler, S. The chromosome number in humans: a brief history. Nat Rev Genet 7, 655–660 (2006).

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