The Woman who Silenced Genes – Lyonization

Mary Lyon

(1925-2014)

Mary Lyon was educated in Britain during World War II, not an easy time for women to study. Fewer educational positions were open to women and women only received ‘titular’ degrees despite attending the same classes as men. In this environment Mary Lyon attended both Girton College and Cambridge University and became a geneticist by way of embryology.

Her interest in embryology was sparked by the work of C.H. Waddington. At this time genetics was not even offered as a course! She decided to pursue a PhD and joined the lab of R.A. Fisher but before finishing moved to Edinburgh and joined D.S. Falconer’s lab where she completed her degree. Thus her academic pedigree is a who’s who of genetic titans.

In Edinburgh, she joined the MRC radiobiology unit in Harwell where she was active from 1962 to 1987. Dr. Lyon’s research made a massive contribution to biology in general through her discovery of X-chromosome inactivation.

Using mutant ‘mottled’ mice she carefully conducted breeding experiments and described what is now known often as ‘Lyonization’. Published as a sole author in Nature in 1961 ‘Gene action in the X-chromosome of the mouse (Mus musculus L.)’ demonstrated that in the somatic other X chromosome was silent. Dr. Lyon explored the implications of her discovery (X-inactivation) for various aspects of mammals including development. Her discovery led her to a long-term path of research trying to understand the dynamics of X-inactivation and the evolution thereof. However, her work was by no means on this topic alone. Lyon also studied the biology of sperm and how reproductive organs differentiate between male and female embryo, as well as other aspects of chromosome expression including abnormalities in various strains of mice. Much of her work was with radiation-induced mutant mice. Even after retirement she still worked in her lab.

Dr. Lyon became a Fellow of the Royal Society in 1973 and has an award named for her offered by the British Genetics Society. [Photo from Gitschier, J. 2010. The gift of observation: an interview with Mary Lyon. PLoS Genet 6(1):e1000813.doi:10.1371/journal.pgen.1000813. Open Access]