Gene pool
The gene pool denotes the totality of all gene variations ( alleles ) in a population and is a term used in population genetics and population ecology . If there is only one allele for a particular gene in the entire population, the population for this gene location is monomorphic . If there are several / many different versions of the gene in the population, it is polymorphic for this gene .
If the organisms under consideration have more than one set of chromosomes , the total number of alleles in the gene pool can be greater than the number of organisms. However, the actual number of alleles is usually much lower. In the case of severe inbreeding , there can be monomorphic populations with only one version of a particular gene in the entire population. Similar effects also occur with natural forms of strong selection. Usually, not only the selected gene itself, but also a more or less broader adjacent area of the DNA is characterized by a remarkably low variability compared to the rest of the genome. This is due to the fact that the selection does not start on the isolated gene itself, but on a section of the chromosome in question (containing the actually selected gene) that is randomly delimited by recombination . This effect is called "genetic sweep" (roughly: genetic wiping).
A measure of the size of a population's gene pool is the effective population size , abbreviated as Ne . A human population with its diploid set of chromosomes theoretically has a maximum of twice as many alleles of a gene as individuals, that is: Ne ≤ 2 * N (the actual population size). Except for the sex chromosomes .
The size of the gene pool of a species is variable over time. Factors that increase the gene pool are mutations and introgression (crossing of alleles from related populations or species). Selection and gene drift , on the other hand, reduce the gene pool, selection in a directed way, gene drift in a random way. When none of these factors are effective, the gene pool remains constant from generation to generation, this is known as the Hardy-Weinberg equilibrium .
A larger gene pool with many different variants of individual genes means that the descendants of a population are better adapted to a changed environment. The allele frequency can adapt to such changes much more quickly if the corresponding alleles are already present than if they had to be created anew through mutation . Conversely, it can be advantageous to have the smallest possible gene pool in an environment that always remains the same, so that too many unfavorable allele combinations do not arise by chance.
In plant breeding, a distinction is made between a primary, secondary and tertiary gene pool. The primary gene pool includes one cultivated species and other species that can easily be crossed . The secondary gene pool also includes species that can only be crossed with difficulty, and the tertiary gene pool includes other species that can only be crossed using special methods such as embryo culture.
history
The Russian geneticist Alexander Serebrovsky formulated the concept of the gene pool ( genofond ) in the Soviet Union in the 1920s. Theodosius Dobzhansky brought the concept to the USA and translated it as "gene pool".
Use in breeding
By breeding , especially by inbreeding, unwanted genes can be bred out of the gene pool. The population then becomes more homogeneous in terms of desired traits. However, due to too many monomorphic gene loci and thus reduced adaptability to changing environmental conditions, such inbred lines tend to inbreeding depression . By crossing with individuals of other varieties, the fitness and the yield can increase significantly ( heterosis effect ). The size of the gene pool can be increased by crossing in individuals who do not belong to the population.
Individual evidence
- ↑ Classical breeding and genetic diversity
- ↑ pflanzenforschung.de gene pool
- ↑ Loren Graham: Lonely Ideas: Can Russia Compete? . MIT Press, 2013, ISBN 978-0-262-01979-8 , p. 169.