Gene pool
The gene pool refers to the totality of all gene variations (alleles) in a population and is a term used in population genetics and population ecology. If only one allele exists for a particular gene in the entire population, the population is monomorphic for this gene locus. If several/many different versions of the gene exist 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 may be greater than the number of organisms. In most cases, however, the actual number of alleles is much lower. In the case of heavy inbreeding, monomorphic populations can occur with only one version of a particular gene in the entire population. Similar effects occur in natural forms of strong selection. In most cases, not only the selected gene itself, but also a more or less broad adjacent region of DNA is characterized by strikingly low variability compared to the rest of the genome. This is due to the fact that selection does not start at the isolated gene itself, but at a section of the chromosome in question (containing the actual selected gene), which is randomly limited by recombination. This effect is called "genetic sweep".
A measure of the size of the gene pool of a population is the effective population size, abbreviated as Ne. A human population with its diploid chromosome set thus theoretically has at most twice as many alleles of a gene as individuals, i.e. Ne ≤ 2 * N (the actual population size). Excluding 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 in alleles from related populations or species). Selection and gene drift, on the other hand, decrease the gene pool, selection in a directed manner, gene drift in a random manner. When none of these factors is operative, the gene pool remains constant from generation to generation, this is known as Hardy-Weinberg equilibrium.
A larger gene pool with many different variants of individual genes means that the descendants of a population can be better adapted to a changed environment. The allele frequency can adapt much more quickly to such changes if the corresponding alleles are already present than if they first have to be created by mutation. Conversely, it can be advantageous to have as small a gene pool as possible in an environment that always remains the same, so that too many unfavourable 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 cultivar and other species that can be crossed without difficulty. The secondary gene pool also includes species that can only be crossed with difficulty, and the tertiary gene pool includes further species that can only be crossed with special procedures such as embryo culture.
History
The Russian geneticist Alexander Serebrowski 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".
Application in breeding
Through breeding, especially inbreeding, undesirable genes can be bred out of the gene pool. The population then becomes more homogeneous with respect to desired traits. However, due to too many monomorphic gene loci and thus reduced adaptability to changing environmental conditions, such inbred lines tend towards inbreeding depression. Crossing with individuals of other varieties can then greatly increase fitness and yield (heterosis effect). By crossing in individuals not belonging to the population, the size of the gene pool can be increased.
