The genotype ( ancient Greek γένος génos "genus, sex" and τύπος týpos "shape, image, pattern") is the totality of the genes of an organism or the hereditary image of this living being. It represents the exact genetic makeup of the individual, which includes all of the genetic make-up in this individual.
In eukaryotes , the genotype includes both the genes in the chromosomes of the cell nuclei and extrachromosomal DNA such as the genes of the mitochondrial DNA and, in plants, also the DNA of the chloroplasts . In the prokaryotes , the genes are in a nucleoid or plasmid .
The individual genotype forms the genetic basis for the development of the morphological and physiological characteristics of the individual through gene expression , which determine the phenotype . In the diploid organisms that arise through sexual reproduction, the genotype also includes hereditary factors that are recessive and have less or no influence on the phenotype if they are heterozygous . The genetic information on introns also belongs to the genotype without affecting the phenotype, because only the genetic information on the exons can be activated and read off during protein synthesis. The genotype as the entirety of the genetic makeup is also significant insofar as one gene alone cannot ensure the development of a characteristic, but rather the interaction of many genes in a chronological sequence. Here, however, the presence or absence of an allele can definitely play a decisive role in whether a characteristic can be developed or not.
Concept formation and use
The term genotype was coined in 1909 by the Danish geneticist Wilhelm Johannsen . Today it is mainly used in connection with Mendel's theory of inheritance and when evaluating the results of a DNA analysis , but here - not entirely in accordance with the original definition - with reference to only those hereditary traits that are of interest in the examination.
The genetic information of the entire cell is used as idiotype or idiotype designated ( ancient Greek ἴδιος idios "intrinsically, especially"). Two organisms whose genes only differ in one gene locus (= one position in their genome ) have a different genotype. The term “genotype” thus refers to the complete combination of all alleles / all loci of an organism. The phenotype is the sum of all observable characteristics of the organism (e.g. size, flower color, beak shape) that have developed as a result of the interaction of the genotype with the environment. The genotype does not change during the lifetime of an organism, except for extreme influences such as e.g. B. mutagenic radiation or temperature shocks.
Organisms of identical genotype also usually differ in their phenotype. Epigenetic mechanisms are responsible for this , i. H. identical genes can be expressed differently in different organisms (see also modification ).
A common example is monozygous (identical) twins . Identical twins share the same genotype because they share the same genome. However, identical twins can be identified by their fingerprints , which are never exactly the same. In the course of life they can develop a different phenotype.
The concept of phenotypic plasticity describes the extent to which the phenotype of an organism is predetermined by its genotype. A high value for plasticity means: environmental influences have a strong influence on the individually developing phenotype. If plasticity is low, the phenotype can be reliably predicted from the genotype, regardless of special environmental conditions during development. High plasticity can be observed in the example of the larvae of the newt : When these larvae perceive the presence of predators such as dragonflies , the head and tail enlarge in relation to the body and the skin is pigmented darker . Larvae with these traits have better chances of survival than predators , but grow more slowly than other phenotypes.
- Richard Lewontin : The Genotype / Phenotype Distinction. In: Edward N. Zalta (Ed.): Stanford Encyclopedia of Philosophy .
- Katharina Munk, Dieter Jahn : Genetics. Georg Thieme Verlag, 2010, ISBN 978-3-13-144871-2 , p. 254.
- Jan Murken: Human Genetics. Georg Thieme Verlag, 2006, ISBN 978-3-13-139297-8 , p. 73.
- Virgine Orgogozo, Baptiste Morizot, Arnaud Martin: The differential view of genotype-phenotype relationships Frontiers in Genetics 2015
- Georg Toepfer: Historical dictionary of biology. Springer-Verlag, 2016, ISBN 978-3-476-00455-0 , p. 59.