Population bottleneck
As a genetic bottleneck is referred to in population genetics is a strong genetic impoverishment of a kind and the associated change in allele frequencies, which is caused by reduction to a very small, often consisting only of a few individuals population (founder effect).
Upon receiving highly endangered species this can be a major problem if a reproduction impairs allele can not be compensated by a second, more favorable for the reproduction allele (see recessive hereditary disease ). A genetic bottleneck can therefore have inbreeding depression result.
Occurrence of genetic bottlenecks
Wild Animals
Several species have gone in the last two hundred years by genetic bottlenecks or just go through such passes, including the David Hirsch, the California condor ( Gymnogyps californianus ), the Arabian oryx (Oryx leucoryx ), the Alpine ibex (Capra ibex), the kakapo ( Strigops habroptilus ), the European bison (Bison bonasus ) and the Przewalski's Horse (Equus przewalski ). In the above cases go all animals living today back on numbers of about a dozen to a hundred individuals. The cheetah (Acinonyx jubatus ) is gone in prehistoric times by a so extremely narrow genetic bottleneck that today tissues can be transferred from a cheetah to any other without rejection, which is only in monozygotic twins is otherwise possible.
When zoo animals, from which one can keep only a few individuals for reasons of space - such as elephants or rhinoceroses - are genetically distinct breeding animals consuming imported from other zoos to maintain genetic diversity and avoid inbreeding. Even more important is this consideration when breeding animals should be reintroduced.
Pet Breeding
Also in the breeding of domestic animals are genetic bottlenecks are not uncommon and occur especially in purebred dogs, purebred cats and small domestic animals (eg hamsters ) on. This has especially in dogs and cats mean that certain rare inherited diseases in certain breeds occur very frequently in the whole population.
In establishing an inbred genetic bottleneck is intentionally induced to reduce the variability of the phenotype, as far as possible within the line.
Genetic bottleneck in humans
Statistical analyzes of mitochondrial DNA ( mtDNA) of anatomically modern humans (Homo sapiens) have revealed an unexpectedly low genetic diversity and led to the assumption that there might have been a genetic bottleneck in humans approximately 70,000 to 80,000 years ago. At that time, therefore, had only about 1000-10000 individuals of Homo sapiens, mostly lived in Africa.
After a controversial hypothesis, the anthropologist Stanley Ambrose ( Toba catastrophe theory ), this genetic bottleneck due to the super- eruption of Toba in Sumatra about 74,000 years ago. This eruption was an extreme cold period followed ( volcanic winter), the Homo sapiens have brought to the brink of extinction. This hypothesis combines two conflicting findings on the genetic evolution of Homo sapiens: On the one hand, beginning in Africa, a relatively rapid propagation of man through fossils assignable, which can also be detected on the basis of mitochondrial differences. Both can be used to explain the very low genetic variability of humans living today (see mitochondrial Eve and Adam of the Y chromosome ). Secondly, there is the view that after the first spread a regionally different, isolated development of the populations occurred, which resulted in the appearance of the people began to differentiate what prompted earlier anthropologists to define various so-called large breeds and breeds.
In another study, it was calculated that 1.2 million years ago lived only about 18,500 individuals out of the direct line ancestors of Homo sapiens.