Mary Frances Lyon | Biography

Mary Lyon's research in mouse genetics has contributed to the understanding of human genetic inheritance. Her discovery of X-chromosome inactivation, the process whereby one of the two X chromosomes in females becomes inactive early in embryonic development, furthered the understanding of the types of diseases that arise from X chromosomal genetic mutations. She has been responsible for advances in the field of environmental mutagenesis and has pioneered novel ways of assessing the risks posed from chemical mutagens.

Mary Lyon was born in England in 1925. She studied at Cambridge University, where she received a B.A. degree in 1946, and her Ph.D. in 1950. From Cambridge she moved to the Medical Research Council Radiobiological Unit in Harwell, England, where she remains. From 1962 to 1986, Lyon headed the unit.

In 1962, Lyon proposed the Lyon Hypothesis (now considered as the Lyon Principle) to explain why the phenotypic effect of the X chromosome is the same in the mammalian female that has two X chromosomes, as it is in the male that has only one X chromosome. The hypothesis proposed that one of the two female X chromosomes is selected at random and inactivated early in embryonic development. Subsequent research has confirmed her proposal. It is now known that, once an X chromosome has been randomly inactivated, the same chromosome continues to be inactivated in all the cells derived from the first cell. Furthermore, it is now known that only parts of the affected X chromosome are inactive; certain areas crucial to development remain active. Usually late replicating, these active areas area condensed and can be visualized microscopically, and are called X chromatin, or Barr bodies. The identification of this structure used to form the basis of gender identification tests in athletic competitions, as males lack a Barr body.

The verification of the Lyon Hypothesis has afforded crucial insight into the processes and evolution of sexual differentiation and made "Lyonization" a model system for the study of how cells read their genetic code.

Among her awards and honors are the Royal Medal of the Royal Society and the Wolf Prize in Medicine. Currently, the Mary Lyon Centre of Excellence in the study of new mouse models of human disease is being established in Harwell. The facility will be commissioned in the autumn of 2002.

Recent Updates

May 3, 2004: Lyon was awarded the 2004 March of Dimes Prize in Developmental Biology "for her discovery of X-chromosome inactivation, one of the first great insights into genetic control mechanisms in the twentieth century and a key to understanding the nature of X-linked birth defects--such as hemophilia, Duchenne muscular dystrophy, and fragile X syndrome--and certain types of cancer." The prize carries a $250,000 award. Source: Newswise, www.newswise.com, May 4, 2004.

May 3, 2004: Lyon was awarded the 2004 March of Dimes Prize in Developmental Biology "for discovery of X-chromosome inactivation. This was one of the first great insights into genetic control mechanisms in the twentieth century and was key to understanding the nature of X-linked birth defects, such as hemophilia, Duchenne muscular dystrophy, and fragile X syndrome, as well as certain types of cancer." The prize, including a $250,000 cash award and a silver medal, was awarded in San Francisco, California. Source: EurekAlert!, www.eurekalert.org, August 24, 2004; March of Dimes, www.marchofdimes.com, August 24, 2004.