X Inactivation Discoverer Dies

British geneticist Mary Lyon has passed away at age 89.

Jan 9, 2015
Jenny Rood

WIKIMEDIA, JANE GITSCHIERMary Lyon, “one of the foremost geneticists of the 20th century” according to a statement by the Medical Research Council (MRC) Harwell, died last month (December 25). She was 89.

Lyon graduated from the University of Cambridge in 1946, a time when women did not officially receive degrees from the institution. She went on to pursue a PhD with R.A. Fisher in Cambridge and Conrad Hal Waddington in Edinburgh, completing her thesis in 1950. She then continued as a postdoc in Waddington’s lab, studying the mutagenic effects of radiation in mice, before moving to her own facility at MRC Harwell in 1955. Lyon headed up the genetics section there from 1962 to 1987.

In 1961, she developed the idea of X-chromosome inactivation, the random switching off of one of the two X chromosomes in each cell of female animals, from her studies of X-linked mutations in the mouse mottled gene, which affects fur color. “The female mouse only needs one X chromosome, and in female mice the X chromosome behaves strangely.  So I put all those things together and came up with the idea of X-chromosome inactivation,” Lyon recalled in a 2010 interview with PLOS Genetics. The process of X-inactivation is also known as “lyonization” in honor of her theory.

 “In her own quiet way, she was a tremendous inspiration and supporter of young scientists and all those who were starting out a career in genetics,” the MRC Harwell statement said. The Mary Lyon Centre of MRC Harwell, a facility for mouse functional genomics study, was founded in 2004.

Lyon was also renowned for her work on the t-complex and her mouse genetics advocacy. “She was among the first to recognize the importance of mouse mutants both as potential models of human disease and for investigating biological processes,” according to a profile by the European Cytogeneticists Association. Lyon was a Royal Society Fellow and won several awards, including the Royal Medal of the Royal Society in 1984 and the Wolf Prize in Medicine in 1997.