Mary Frances Lyon (1925–2014) was an English geneticist

Lyon is best known for her discovery of X-chromosome inactivation. Lyon proposed her hypothesis on the behaviour of X chromosomes in XX females in 1961, originally to explain her findings on the coat colour of mice carrying sex-linked colour genes.

Lyon also made significant contributions to understanding environmental mutagenesis.

  • Born on May 15, 1925 in Norwich, England
  • 1946 – BA, Cambridge University
  • 1948 – ScD, Cambridge University
  • 1950 – Doctorate
  • 1962 – Head of the Genetics section of the Radiobiology unit
  • 1973 – Fellow of the Royal Society, FRS
  • US National Academy of Sciences Royal Medal (1984), the Wolf Prize for Medicine (1997) and the Pearl Meister Greengard Prize (2006)
  • Died on Dec 25, 2014 in Drayton, England aged 89 years

Medical Eponyms
Lyon hypothesis (1961)

Through her mutagenesis experiments on mottled mice and building on recent discoveries that only one X chromosome is required and that sex chromatin consists of highly a condensed X chromosome (Susumo Ohno), Lyon came to build her hypothesis: that only one X chromosome in a cell is active, due to random inactivation of one of the two X chromosomes, early in embryological development and that the inactivation is permanent and mitotically stable. The inactivated X chromosome is condensed down and seen as sex chromatin (Barr body).

It is here suggested that this mosaic phenotype is due to the inactivation of one or other X-chromosome early in embryonic development. If this is true, pigment cells descended from cells in which the chromosome carrying the mutant gene was inactivated will give rise to a normal-coloured patch and those in which the chromosome carrying the normal gene was inactivated will give rise to a mutant-coloured patch

Lyon 1961

Lyonisation (Miller and Boscoe, 1963)
The inactivation of an X chromosome as first hypothesized by Mary Lyon. We now know X-inactivation involves a number of different mechanisms including DNA methylation, RNA-mediated gene silencing, and changes in chromatin modification/organization.

Mary Lyon medal of the UK Genetics Society (2014)
Established in 2015 to reward outstanding research in genetics to scientists who are in the middle of their research career

Major Publications




Studied at Univerisity of Cambridge - BA MB BChir. British doctor working in emergency medicine in Perth, Australia. Special interests include primary care and emergency medicine.

BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Emergency physician, Sir Charles Gairdner Hospital.  Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |

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