Roll-Hansen, N. Sources of Johannsen's Genotype Theory: Nils Roll-Hansen. Conference A Cultural History of Heredity III : 19th and early 20th centuries.(2005).

Roll-Hansen, Nils. "Sources of Johannsen's Genotype Theory: Nils Roll-Hansen." Conference A Cultural History of Heredity III : 19th and Early 20th Centuries.(2005) .

Roll-Hansen, Nils. "Sources of Johannsen's Genotype Theory: Nils Roll-Hansen." Conference A Cultural History of Heredity III : 19th and Early 20th Centuries.(2005), .