Back mating
A back mating is a mating made possible by a breeder of an animal of a daughter generation (F1 generation) with an animal of the P generation , i.e. with the father or mother of the animal. Genetic back-crossing occurs through back-breeding . Back-mating or back-crossing are thus forms of inbreeding that are used to produce inbred lines . In a Rückverpaarung with respect to a desired characteristic homozygous parent with 50% in this regard homozygous progeny can be expected, while with a Geschwisterverpaarung after the splitting rule ( Mendelian Inheritance ) are to be expected only 25%.
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With plants
In the case of flowering plants , backcrossing through insect or wind pollination can happen by chance if pollen from the mother or father plant or pollen from a plant of the offspring generation reaches the female flower organ ( pollination ) and fertilization of the plant egg takes place, so that the F2 offspring from one each P-generation and F1-generation plants emerge. Plant breeders can make targeted backcrosses through artificial pollination. Since there is no pairing of individuals in plants, but only their gametes unite, only backcrossing is used here .
Behavioral aspects in animals
In the case of fish , amphibians , reptiles and mammals , mating back may happen by chance, as they are just as unaware of their degree of relationship as they are of the fact that offspring will be produced by mating .
When in patriarchal structured packs mammals in a hierarchy have, in which the highest-ranking male animal in the mating season copulated almost all females and rivals are marketed such as in red deer , it is the norm that later met his female offspring of her sire become. The same was observed in the mating behavior of gorillas . Mammals living in matriarchal packs, such as the bonobo , mate mothers with their male offspring.
In the case of wolves , in which only a single pair consisting of the lead wolf and lead wolf father the offspring, while the reproduction of the other pack members is suppressed, after the death of the lead wolf, one of his sons can take his place in the hierarchy and then also the lead wolf , so his mother animal, cover.
Genetic Aspects
Back mating with high-ranking individuals lead to the increased passing on of genetic traits for physical characteristics as well as instinctive behavioral characteristics that have proven themselves in the respective habitat and within the pack.
Effects in recessive genes
In diploid organisms that are created through sexual reproduction , a great number of genetic traits are inherited according to Mendel's rules . Recessive hereditary factors are therefore by the after Rückverpaarung in the progeny backcross heaped homozygous and thus also in the phenotype frequently occur. Since natural selection starts with the individual, back mating in nature leads to unfavorable recessive hereditary dispositions and recessive hereditary diseases appearing phenotypically, and the selection can mean that the affected individuals usually produce fewer or no offspring at all. However, this does not change the proportion of conductors within the population who do not have the characteristic but still pass them on.
For a long time, inbreeding was mistakenly assumed to be the cause of the diseases that occur more frequently in homozygous offspring, on the assumption that unknown biological factors would trigger the diseases in relative matings.
However, thanks to the discoveries of Gregor Mendel and molecular genetic research, we now know that such diseases, which are mostly caused by genetic defects and often appear phenotypically in related matings, are the expression of recessive alleles , and that these are from healthy heterozygous individuals ( Conductors ) can also be passed on unnoticed (recessive) with unrelated, genetically healthy partners. We also know today that if there are no genes for hereditary diseases at all, they cannot be inherited.
In animal breeding , mating can be carried out in order to check in advance the presence of recessive undesirable or disease-causing genetic makeup in animals that may be used for breeding. This questionable method, in which it is accepted that sick young animals may also be born, can now be replaced by DNA analysis . However, mating back can also be carried out in order to show the desired recessive genetic makeup phenotypically in order to continue breeding with the pure-breeding carriers of the desired trait.
Effects in dominant genetic makeup
The dominant hereditary diseases also appear in heterozygous individuals, so that the natural selection or the breeding selection of the breeder can begin directly. Since they are recognizable by the phenotype for the breeder, the carriers of the trait can be excluded from breeding immediately. If an undesirable genetic trait has already spread within a race and barely individuals are available that do not have the feature, it is possible that undesirable feature by one to bring Rückverpaarung with a (homozygous) healthy breeder and subsequent selective breeding to disappear because one can breed heterozygous offspring, of which 50% of the offspring in the F2 generation do not have the undesired allele after a back-mating, i.e. are genetically healthy or genetically-inherited carriers of the desired trait.
Breeding responsibility
Continued inbreeding but also normal selection breeding over many generations can lead to a depletion of the gene pool , whereby vitality genes can also be lost. That is why breeders prefer matings with unrelated or distantly related animals.
In order to exclude all risks as in the pedigree of an animal, recessive hereditary diseases that have not appeared phenotypically anywhere or undesirable recessive hereditary factors such as false colors , animal breeders are increasingly making use of the possibility of a preventive DNA test .
In most breeders' associations, depending on the species of animal, mating back for the purpose of pure breeding (also line breeding ) is either only permitted with restrictions or is prohibited. In cats is a Rückverpaarung allowed, between an animal of the P and one of the F1 generation, others are prohibited. There are no restrictions on the breeding of ornamental fish in the aquarium hobby.
See also
Individual evidence
- ↑ Ulrich Weber: Biologie Oberstufe complete volume, Cornelsen-Verlag, Berlin 2001, pp. 168–171. ISBN 3-464-04279-0
- ↑ https://www.gesetze-im-internet.de/tierschg/BJNR012770972.html
- ↑ http://www.tieraugendoc.at/wissenswertes/tr%C3%A4nendes-auge-epiphora/
- ↑ http://www.laboklin.de/index.php?link=labogen/pages/html/de/erbkrankheiten.html