Gregor Mendel (1822-1884) was an Austrian monk whose experimental work became the basis of modern hereditary theory. As a substitute teacher at the technical school in Brünn, Mendel became actively engaged in investigating variation and heredity in plants at the monastery's experimental garden.

Between 1856 and 1863 he cultivated and tested at least 28,000 pea plants, carefully analyzing seven pairs of seed and plant characteristics. His tedious experiments resulted in the enunciation of two generalizations that later became known as the laws of heredity. His observations also led him to coin two terms still used in present-day genetics: dominance, for a parents' trait that appears up in the offspring; and recessiveness, for a trait masked by a dominant gene. Mendel published his important work on heredity in 1866. Despite its descriptions of large numbers of experimental plants, which allowed him to express his results numerically and subject them to statistical analysis, this work made virtually no impression for the next 34 years.

In 1900 was his work recognized more or less independently by three investigators, one of whom was the Dutch botanist Hugo De Vries, and not until the late 1920s and the early '30s was its full significance realized, particularly in relation to the theory of evolution. As a result of years of research in population genetics, investigators were able to demonstrate that Darwinian evolution can be described in terms of the change in gene frequency of Mendelian pairs of characteristics in a population over successive generations. Mendel's later experiments with the hawkweed Hieracium proved inconclusive, and because of the pressure of other duties he ceased his experiments on heredity by the 1870s.