Wilhelm Johannsen

Danish pharmacist, botanist, plant physiologist, and geneticist.

- Wilhelm Johannsen

30 related topics

Gene

Basic unit of heredity and a sequence of nucleotides in DNA that encodes the synthesis of a gene product, either RNA or protein.

Fluorescent microscopy image of a human female karyotype, showing 23 pairs of chromosomes. The DNA is stained red, with regions rich in housekeeping genes further stained in green. The largest chromosomes are around 10 times the size of the smallest.

Schematic of a single-stranded RNA molecule illustrating a series of three-base codons. Each three-nucleotide codon corresponds to an amino acid when translated to protein

Protein coding genes are transcribed to an mRNA intermediate, then translated to a functional protein. RNA-coding genes are transcribed to a functional non-coding RNA.

Inheritance of a gene that has two different alleles (blue and white). The gene is located on an autosomal chromosome. The white allele is recessive to the blue allele. The probability of each outcome in the children's generation is one quarter, or 25 percent.

A sequence alignment, produced by ClustalO, of mammalian histone proteins

Depiction of numbers of genes for representative plants (green), vertebrates (blue), invertebrates (orange), fungi (yellow), bacteria (purple), and viruses (grey). An inset on the right shows the smaller genomes expanded 100-fold area-wise.

Gene functions in the minimal genome of the synthetic organism, Syn 3.

Comparison of conventional plant breeding with transgenic and cisgenic genetic modification.

The term gene was introduced by Danish botanist, plant physiologist and geneticist Wilhelm Johannsen in 1909. From p. 124: "Dieses "etwas" in den Gameten bezw. in der Zygote, … – kurz, was wir eben Gene nennen wollen – bedingt sind." (This "something" in the gametes or in the zygote, which has crucial importance for the character of the organism, is usually called by the quite ambiguous term Anlagen [primordium, from the German word Anlage for "plan, arrangement ; rough sketch"].

Genotype

Organism is its complete set of genetic material.

An example of a pedigree for an autosomal dominant condition

An example of a pedigree for an autosomal recessive condition

The term genotype was coined by the Danish botanist Wilhelm Johannsen in 1903.

Phenotype

Set of observable characteristics or traits of an organism.

Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal color in pea plants. The letters B and b represent genes for color, and the pictures show the resultant phenotypes. This shows how multiple genotypes (BB and Bb) may yield the same phenotype (purple petals).

ABO blood groups determined through a Punnett square and displaying phenotypes and genotypes

Biston betularia morpha typica, the standard light-colored peppered moth

B.betularia morpha carbonaria, the melanic form, illustrating discontinuous variation

Wilhelm Johannsen proposed the genotype–phenotype distinction in 1911 to make clear the difference between an organism's hereditary material and what that hereditary material produces.

Royal Veterinary and Agricultural University

The Royal Veterinary and Agricultural University (Kongelige Veterinær- og Landbohøjskole, abbr.

Wilhelm Johannsen (1857–1927)

University of Copenhagen

The University of Copenhagen (Københavns Universitet, abbr.

The Round Tower (Rundetårn), used as an observatory by astronomer Ole Rømer.

Interior of the old university library at Fiolstræde around 1920.

The seal of 1531 (left) and the seal of 1537 (right)

The oldest surviving lecture plan from the university is from 1537.

Wilhelm Johannsen (1857–1927), Danish botanist, first coined the word gene in its modern usage.

Mutationism

One of several alternatives to evolution by natural selection that have existed both before and after the publication of Charles Darwin's 1859 book On the Origin of Species.

Painting of Hugo de Vries, making a painting of an evening primrose, the plant which had apparently produced new forms by large mutations in his experiments, by Thérèse Schwartze, 1918

Étienne Geoffroy Saint-Hilaire believed that "monstrosities" could immediately found new species in a single large jump or saltation.

Rudolph Albert von Kölliker revived Geoffroy's saltationist ideas, calling his theory heterogenesis. It depended on a nonmaterial directive force (orthogenesis).

Drawing of William Bateson, 1909, by the biologist Dennis G. Lillie

Wilhelm Johannsen's "pure line" experiments seemed to show that evolution could not work on continuous variation.

Papilio polytes has 3 forms with differing wing patterns, here the "Romulus" morph. Reginald Punnett argued that this polymorphism demonstrated discontinuous evolution. However, Ronald Fisher showed that this could have arisen by small changes in additional modifier genes.

Thomas Hunt Morgan's work on Drosophila melanogaster found many small Mendelian factors for natural selection to work on.

John Christopher Willis's The Course of Evolution by Differentiation Or Divergent Mutation Rather Than by Selection, 1940

Masatoshi Nei argues that evolution is often mutation-limited.

Wilhelm Johannsen's "pure line" experiments on Phaseolus vulgaris beans appeared to refute this mechanism.

Pangenesis

Charles Darwin's hypothetical mechanism for heredity, in which he proposed that each part of the body continually emitted its own type of small organic particles called gemmules that aggregated in the gonads, contributing heritable information to the gametes.

De Vries also coined the term 'pangene' which 20 years later was shortened by Wilhelm Johannsen to gene.