The discovery of transposons by Barbara McClintock is a foundation of epigenetics. Transposons and their epigenetic modifications define non-transcribed regions of the genome termed heterochromatin, and their deregulation is associated with cancer. The origin of the term heterochromatin has become obscure — it was defined by Emil Heitz (1892–1965) in the first half of the 20th century.

In 1928, Heitz improved a cytological staining method and discovered that certain parts of mitotic chromosomes are more densely stained than others, thereby defining heterochromatin and euchromatin, respectively. The work was performed in liverworts, of which a model organism is Marchantia polymorpha. The compartmentation of chromatin was documented by Heitz in >70 species of bryophytes and in >70 species of flowering plants.

Research by Thomas Morgan on heredity encouraged Heitz to extend his investigation of heterochromatin to insects. In 1932 and 1933 he showed in plants and animals that sex chromosomes comprise more heterochromatin than autosomes do. With H. Bauer he also identified the nature of polytene chromosomes, with their specific pattern of heterochromatin, in march flies, a discovery that later had a great impact on defining the nature of genes in fruit flies.

Heitz … discovered that certain parts of mitotic chromosomes are more densely stained than others

As early as 1929, Heitz proposed that heterochromatin is enriched in parts of chromosomes that do not carry genes or is associated with genetically ‘passive’ regions; this is still the basis of the contemporary definition of heterochromatin. The work of Heitz led to outstanding advances in understanding the links between genetics, development and heredity at a time when the molecular nature of the heredity material was still unclear.

Despite these contributions, Heitz is largely unknown and he is hardly ever mentioned in chromatin and epigenetics meetings. In part this is because his work was published in German and has never been translated. His obscurity could also be attributed to his dismissal from his professorship at the University of Hamburg in 1937, because his maternal grandfather was of Jewish descent. The dismissal disrupted his research for nearly 15 years and, despite a new appointment in Tübingen in 1952, Heitz did not resume his work on chromatin.

The unfortunate trajectory of the career of Emil Heitz can teach us at least two lessons: key findings are often made in studies of non-model organisms and the increasing feasibility of genome sequencing should trigger funding for research in such organisms; and the fate of Heitz in 1930s’ Germany should alert us to the dangers of current nationalistic tendencies, which are fundamentally incompatible with science.