She was a famous mouse geneticist who spend most of her working career at the MRC labs in Harwell, United Kingdom (near Oxford). The labs are known as an international center for mouse genetics.
Mary Lyon is famous for discovering the phenomenon of X chromosome inactivation. This is when one the the X chromosomes of female mammals is selectively inactivated so that the products of the X chromosome genes are quantitatively similar to the dosage in males where there's only one X chromosome. The phenomenon used to be referred to as Lyonization.
I never met Mary Lyon but from what people say about her, I'm sure I would have liked her. Here's an excerpt from the obituary in Nature: Mary F. Lyon (1925 - 2014).
Lyon was a central figure in twentieth-century mouse genetics. She laid the intellectual foundations and developed the genetic tools for the use of mice as model organisms in molecular medicine, cell and developmental biology and in deciphering the function of the human genome. Lyon was editor of Mouse News Letter from 1956 to 1970, a publication that had a key role in establishing a mouse-focused research community in the pre-Internet age. She also helped to develop a common language for the field by chairing the Committee on Standardised Genetic Nomenclature for Mice from 1975 to 1990. Her pivotal contribution was recognized by the naming of the Mary Lyon Centre, an international facility for mouse-genetic resources, opened at Harwell in 2004, and by the creation of the Mary Lyon Medal by the UK Genetics Society in 2014.X chromosome inactivation is one of the classic examples of epigenetics, sensu stricto. It was the subject of one of my most popular posts of all time: Calico cats. Calico cats almost always have to be female but there are very rare examples of male calico cats. Can anyone figure out why?
Because everything Mary said was so carefully thought through, she could be difficult to talk to: on the phone, it was easy to think you had been cut off. She did not suffer fools gladly, but was a great supporter of the bright young scientist, often eschewing authorship of publications to enhance the profile of junior collaborators. She was intellectually rigorous but not dictatorial. When I began my PhD with her in 1977, she gave me a handful of papers, showed me the genetic tools — mice carrying the various mutations and chromosomal rearrangements — and said, “do something on X-inactivation”. That degree of academic freedom was exhilarating, coupled as it was with the safety net of robust critique.
... Her first love was mice, although she always had a cat — a tortoiseshell, of course.