Born in 1925, Mary Lyon is an English geneticist who is best known for her discovery of X-chromosome inactivation (also known as lyonization), which is the process by which one of the two copies of the X chromosome present in female mammals is randomly inactivated.
During WWII, Mary pursued her studies at Girton College at the University of Cambridge, where she studied zoology, physiology, organic chemistry and biochemistry, with zoology as her main subject. During that time she became interested in embryology. She went on to do her PhD with R A Fisher, who was Professor of Genetics in Cambridge, where she characterized a mutant mice strain.
After her PhD, Mary joined the group of Conrad Hal Waddington, funded by the Medical Research Council to investigate mutagenesis and the genetic risks of radiation. She has published many papers on radiation and chemical mutagenesis and on studies of mutant genes. She was head of the Genetics Section of the MRC Radiology Unit at Harwell from 1962 to 1987. She retired from active research in 1990.
In 1961, while working on radiation hazards, Mary Lyon proposed the random inactivation of one female X chromosome to explain the mottled phenotype of female mice heterozygous for coat color genes. The Lyon hypothesis also accounted for the findings that one copy of the X chromosome in female cells was highly condensed, and that mice with only one copy of the X chromosome developed as infertile females. Examples of X chromosome deactivation are calico fur patterns in female cats and Duchenne muscular dystrophy in human males.Â
