An inheritable factor that determines a biological character of an organism is called a gene (functional unit of hereditary material). Mendel called them as factors. Wilhelm Johannsen, a Danish botanist, had given the term "gene" ("gen" in Danish and German) in 1909 while describing these fundamental physical and functional units of heredity. He is also known for coining the terms phenotype and genotype, and for his 1903 "pure line" experiments in genetics. Genotype is the genetic makeup or allelic combination of a living organism.