section_path: History/Discovery of discrete inherited units
section_name: Discovery of discrete inherited units
paragraph_text: Discovery of discrete inherited units
  
  The existence of discrete inheritable units was first suggested by Gregor Mendel (1822–1884). From 1857 to 1864, in Brno, Austrian Empire (today's Czech Republic), he studied inheritance patterns in 8000 common edible pea plants, tracking distinct traits from parent to offspring. He described these mathematically as 2 combinations where n is the number of differing characteristics in the original peas. Although he did not use the term gene, he explained his results in terms of discrete inherited units that give rise to observable physical characteristics. This description prefigured Wilhelm Johannsen 's distinction between genotype (the genetic material of an organism) and phenotype (the observable traits of that organism). Mendel was also the first to demonstrate independent assortment, the distinction between dominant and recessive traits, the distinction between a heterozygote and homozygote, and the phenomenon of discontinuous inheritance.
  
  Prior to Mendel's work, the dominant theory of heredity was one of blending inheritance, which suggested that each parent contributed fluids to the fertilization process and that the traits of the parents blended and mixed to produce the offspring. Charles Darwin developed a theory of inheritance he termed pangenesis, from Greek pan ("all, whole") and genesis ("birth") / genos ("origin"). Darwin used the term gemmule to describe hypothetical particles that would mix during reproduction.
  
  Mendel's work went largely unnoticed after its first publication in 1866, but was rediscovered in the late 19th century by Hugo de Vries, Carl Correns, and Erich von Tschermak, who (claimed to have) reached similar conclusions in their own research. Specifically, in 1889, Hugo de Vries published his book Intracellular Pangenesis, in which he postulated that different characters have individual hereditary carriers and that inheritance of specific traits in organisms comes in particles. De Vries called these units "pangenes" (Pangens in German), after Darwin's 1868 pangenesis theory.
  
  Twenty years later, in 1909, Wilhelm Johannsen introduced the term "gene" and, in 1906, William Bateson, that of " genetics " while Eduard Strasburger, among others, still used the term "pangene" for the fundamental physical and functional unit of heredity.