Under inbreeding is generally understood as the pair relatively close blood relative . In plant breeding , this is done by selfing and crossing relatives that are as close as possible in order to obtain inbred lines that are genetically as pure as possible . In animal breeding , inbreeding takes place through sibling mating and back mating .
The measure of inbreeding is the inbreeding coefficient .
Farm animals and plants
Inbreeding leads to the fact that more and more gene loci or alleles become homozygous (pure hereditary), i.e. are present in the same chromosome set. According to Mendelian rules , recessive genes of the genotype in particular also appear in the phenotype through inbreeding . The consequence of inbreeding is thus the increase in the probability of the homozygous occurrence of extremes in both directions, i.e. both possible pathological and particularly efficient gene combinations.
It is not uncommon for breeders to observe that genetically-inherited organisms have lower vitality and resistance to diseases, since the genetic information is the same in both sets of chromosomes and therefore fewer different genes are present ( inbreeding depression ). On the other hand, breeding consists precisely in using the positive side of inbreeding by combining targeted inbreeding with selection of the appropriate types.
Inbreeding in humans
Avoiding inbreeding ensures the benefits of sexual reproduction .
With numerous animal and plant species, the disadvantages of inbreeding are avoided by dichogamy . Especially with monoecious plants and plants with hermaphrodite flowers is Vormännlichkeit and Vorweiblichkeit observed. This prevents fertilization with its own pollen. In the field of cultivated plants, maize is a representative of pre- masculinity, plantain is a representative of pre-femininity.
In most animal species, incest is only passively avoided by the offspring dispersing or no longer tolerated by the parents, or by the male or female young animals leaving the group; this leads to a spatial separation of the siblings ( exogamy ). These behaviors make mating close relatives unlikely, but they are possible and do happen. The active avoidance of incest is linked to the possibility of individual recognition (recognition) and also occurs in animals. In the case of some bird species (e.g. gray geese ), siblings avoid mating even if they are kept together without other partners; sexual imprinting during early ontogeny plays a role here. In chimpanzees , it has been observed that females actively reject the sexual interest of brothers and that even adult, high-ranking males have no sexual interest in their mother. Research showed that as adults, people have an erotic barrier to those they knew well within the first five years of life.
- Werner Buselmaier, Gholamali Tariverdian: Human Genetics for Biologists , Springer 2006, ISBN 3-540-24036-5
- Volker Storch: Evolutionary Biology , Springer 2001, ISBN 3-540-41880-6
- Rothmaler: Exkursionsflora von Deutschland, Spektrum Akademischer Verlag Heidelberg, Berlin, 20th edition 2011, pp. 25 f., ISBN 978-3-8274-1606-3
- Pre-femininity , Thomas Schöpke, Pharmazie Uni-Greifswald ( Memento from June 23, 2007 in the Internet Archive )