Show Summary Details

Page of

Printed from Oxford Dictionary of National Biography. Under the terms of the licence agreement, an individual user may print out a single article for personal use (for details see Privacy Policy and Legal Notice).

date: 14 October 2019

Lyon, Mary Francesfree

  • Catharine M. C. Haines

Mary Lyon (1925–2014), by unknown photographer, 1950

© Medical Research Council

Lyon, Mary Frances (1925–2014), geneticist, was born on 15 May 1925 at the Maternity Home, 3 Aspland Road, Norwich, the oldest child of Clifford James Lyon (1896–1963), tax office clerk, and his wife, Louise Frances, née Kirby (1893–1986). At the time of her birth registration her parents lived at 96 St Leonard’s Road, Norwich. She went to primary schools in Bradford and Norwich. When the family moved to Birmingham in 1936, she went to King Edward VI High School, where she won four books on wildflowers, birds, and trees in an essay competition set to commemorate the silver jubilee of King George V; her biology teacher was a clear and precise thinker and encouraged her. In 1939 the family moved to Woking and she went to Woking Grammar School for Girls. In the sixth form she studied physics, chemistry, and mathematics, and had to travel to three other local schools. She was given a place at Girton College, Cambridge, and read zoology, physiology, organic chemistry, and biochemistry.

Mary Lyon was awarded a titular degree in 1946 as Cambridge degrees were not awarded to women until 1948. She began her PhD studies with R. A. Fisher, for whom she had scored mouse mutants as an undergraduate. She began by studying mice with the mutant gene pallid and a balance defect. In 1950 she moved to the Institute of Animal Genetics in Edinburgh, which was led by C. H. Waddington. She obtained her PhD the same year and was awarded a Medical Research Council (MRC) grant to work in the team led by Toby Carter, studying the genetic effects of radiation in mice. Edinburgh was a stimulating place to work. In 1955 the team was moved to the MRC Radiology Unit at Harwell, Oxfordshire, where there was more room for expansion. Lyon stayed at Harwell for the rest of her life apart from a brief interlude in 1970–71 when she held a Clothworkers' visiting research fellowship at Girton College, working with Richard Gardner.

In the early years at Harwell, Lyon described the phenomenon of X chromosome inactivation in mammals. This was called 'the Lyon hypothesis', as she was the first to describe the principle of X chromosome inactivation. Lyon published her hypothesis, with evidence, in Nature in 1961. Her hypothesis explained the patchy colour of tortoiseshell cats. The orange colour is X-linked and the coat is a mosaic of cells with either the maternal or paternal X chromosome active. Lyon thought that sixteen days after conception one of the two XX chromosomes in each cell of a female mammal becomes inactive. As a result the dose of X-linked genes in XX females and XY males is equal. Barr bodies found in resting female cells were shown to be the condensed inactive X chromosome. The Lyon hypothesis led to advances in understanding both mouse genetics and the inheritance of certain conditions in humans, such as muscular dystrophy and colour blindness, and it was from this work that epigenetics developed, being partly the way external factors influence the manifestation of certain conditions. She was interested in chromosome 17 and the T-complex found there.

Lyon was head of the genetics division at Harwell from 1962 to 1987 and deputy director of the Radiobiology Unit from 1982 to 1990, when she retired. However she continued to come in to work at Harwell almost daily to continue with her research until some time after she was diagnosed with Parkinson’s disease in 2012. She was elected a fellow of the Royal Society in 1973 and awarded its gold medal in 1984. She was given many other awards such as the Wolf prize for medicine in 1986. She was on the editorial board of several journals, including the Genetical Research Journal, and from 1956 to 1970 was editor of Mouse Newsletter, which became Mouse Genome and later Mouse Newsletter Ltd. In 1996 she co-edited the third edition of Genetic Variants and Strains of the Laboratory Mouse. In 2004 the Mary Lyon Centre was opened at Harwell, which houses hundreds of living mice (the scientists work in a nearby building). She died at her home, Crabtree Cottage, Crabtree Lane, Drayton, Oxfordshire, on Christmas day 2014, from bronchopneumonia and Parkinson’s disease. Her cremation was in Oxford on 16 January 2015.


  • K. T. Butler and H. I. McMorran, eds., Girton College Register, 1869–1946 (1948)
  • B. Cattanach, J. Peters, and T. Searle, ‘Mary Lyon: an appreciation’, Genetics Research, 56 (1990), 83–9
  • C. M. C. Haines, International Women in Science: A Biographical dictionary to 1950 (2001), 185–7
  • D. Bainbridge, The X in sex: how the X chromosome controls our lives (2003)
  • B. R. Migeon, Females Are Mosaics: X Inactivation and Sex Differences in Disease (2007)
  • J. Gitschier, ‘The gift of observation: an interview with Mary Lyon’, PLoS Genetics, 6/1 (Jan 2010), 1–4
  • R. C. Francis, Epigenetics: The Ultimate Mystery of Inheritance (2011)
  • Daily Telegraph (4 Feb 2015)
  • Nature (5 Feb 2015)
  • E. M. C. Fisher and J. Peters, ‘Mary Frances Lyon (1925–2014)’, Cell, 160 (12 Feb 2015), 577–8
  • The Independent (18 Feb 2015)
  • The Guardian (26 Feb 2015)
  • The Lancet (28 Feb 2015)
  • K. Nightingale, ‘Remembering Mary Lyon and her impact on mouse genetics’, Insight [Medical Research Council] (Feb 2015), 1–4
  • S. Rastan, ‘Obituary: Mary F. Lyon (1925–2014)’, Reproductive Biomedicine (2015), 566–7
  • ‘Mary Lyon (1925–2014)’, Staff News, University of Edinburgh, 9 Oct 2015,, accessed 12 Sept 2017
  • WW (2014)
  • personal knowledge (2018)
  • private information (2018) [Janice F. Pittah, niece; P. Glenister; L. Tinsley, librarian, Mary Lyon Centre, Harwell; archivist, King Edward VI Schools, Birmingham]




death certificate
birth certificate
British Library, National Sound Archive