 During the 1950s to 1970s a growing set of observations indicated that determined and differentiated states of cells are transmitted in cell lineages. These observations concerned studies of Drosophila imaginal discs by Ernst Hadorn; Briggs and King’s cloning experiments with amphibians; Mary Lyon’s work on X-chromosome inactivation; and work establishing the in vitro clonal stability of cultured cell lines. Eventually, the term epigenetic inheritance came to refer to hereditary variation that does not involve changes to the DNA sequence.