Gene Pool: History, Primary, Secondary, Tertiary, Quaternary gene pool and Importance
The set of all genes, or genetic data, in any population, typically of a specific species, is known as the Gene Pool
A Gene pool is a collection of all the genes (including alleles) found in a population or species that is capable of reproduction.
The term “Gene pool” refers to the entire gene pool found in interbreeding populations. One way to look at this is that the population’s ability to survive environmental problems increases with the size of the gene pool. Inbreeding can result in a narrow gene pool and a decreased capacity to endure environmental obstacles wherever these people live, such as among siblings or first cousins.
Harlan and De Wet (1971) introduced the idea of a “Gene pool” for the effective and judicious application of germplasm. The idea was first put forth by the Russian geneticist Aleksandr Sergeevich Serebrovskii in the 1920s as “Genofond” (Gene Fund), a term that Theodosius Dobzhansky introduced to the United States from the Soviet Union and translated into English as “Gene Pool.”
According to the degree of relationship, the gene pool of crops can be divided into three groups, (Harlan and De Wet, 1971), viz.
i) Primary gene pool
ii) Secondary gene pool
iii) Tertiary gene pool.
iv) Quaternary gene pool.
A. Primary gene pool
1. This is also referred to as gene pool one (GP 1)
2. The primary gene pool is the one where intermarriage is simple and produces fertile hybrids.
3. It contains plants of the same species or nearly related species that produce fully viable offspring after mating, such as a cross between a wild sunflower and a variety of cultivated sunflowers. a perennial grass in South Siberia known as the winter sunflower species (Helianthus winterii), whose genes are easily transferred to other plant species (H. annus)
4. In such a gene pool, genes can be transferred between lines simply by conducting normal crossings with normal seed sets, segregation, and recombination.
This is the essential breeding component.
It includes two subspecies:
A: Cultivated races
B: Spontaneous races (wild or weedy species)
B. Secondary gene pool
1. These gene pools are also referred to as gene pool two (GP 2)
2. The secondary gene pool is the genetic material that results in partial fertility when GP 1 is crossed with it.
3. It comprises plants from similar species that can’t cross certain barriers with crops.
4. Such materials can be crossed with the primary gene pool, but most hybrids are weak or sterile, and some of the offspring are somewhat fertile, for example, the diploid Aegilops tauschii and A. speltoides, two wild relatives of bread wheat (Triticum aestivum), which are in the secondary gene pool. Since bread wheat is hexaploid, it must contain paired chromosomes.
5. It is possible but challenging to transfer a gene from such material to the primary gene pool, and this can result in several undesirable outcomes, including:
i) Partial sterility or weak hybrids
ii) Chromosomes that pair incorrectly or not at all.
iii) Difficulty in recovering desired phenotypes in succeeding generations.
iv) Plant breeders or geneticists can make use of the gene pool with the necessary effort.
C. Tertiary gene pool
1. This is sometimes referred to as gene pool three (GP 3)
2. The genetic material that causes sterile hybrids to be produced when it is crossed with the primary gene pool is known as the tertiary gene pool.
3. It contains components that can be crossed with GP 1, however, the hybrids are fatal or sterile as a result of aberrant embryonic development
4. It is feasible to transfer genes from such material to the primary gene pool utilizing specialized techniques like embryo culture, tissue culture, chromosomal doubling, or by employing the bridge species (with the members of secondary gene pools)
Aegilops speltoides (BB, 2n=14) and Triticum turgidum (AABB, 2n=28) can both create amphidiploid hybrids (intergeneric cross). Several methods, such as colchicine treatment, can make this fertile. Another successful example is the creation of Triticale by Rimpu, a hybrid between Rye and Wheat (T. aestivum) (Secale cereale).
D. Quaternary gene pool
1. All living things on the planet are now within the range of any crop plant’s germplasm due to recent advances in genetic engineering technology.
2. With the use of advanced recombinant DNA technology, genes can now be transferred not just between species or genera but also between other types of organisms.
3. The ‘Bt’ gene (Transgene) was transferred from a bacterium (Bacillus thuringiensis) to cotton, maize, tomato, and other plant species, expanding the gene pool beyond what is imaginable.
4. As a result, modern science has created a novel sort of gene pool (GP-4), which is sometimes referred to as a “Gene Ocean.”
Why is the gene pool notion important?
Large populations of different wild and indigenous breeds have disappeared in the past, producing severe genetic erosion and genetic pollution. Genetic diversity and overall biodiversity were lost as a result. A specific species or population’s established gene pool may get enriched by the introduction of new genetic variants as a result of immigration. High rates of gene flow can make the genetic differences between the two groups less pronounced and increase homogeneity. Due to this, it has been hypothesized that gene flow limits speciation by mixing the gene pools of the populations and limiting the emergence of genetic differences that would have resulted in full speciation. Through the processes of genetic pollution, such as unchecked hybridization, introgression, and genetic swamping, endemic species may be in danger of going extinct. The uncommon species can breed with the plentiful species, saturating the gene pools.
What is Gene Flow?
Gene flow refers to the transfer of genes. Small pieces of DNA can occasionally be purposely inserted into human transgenic organisms or transferred by pathogenic viruses or other vectors directly into the germline of another person. However, horizontal gene transfer, the term for this type of gene flow, is uncommon. Gene flow is frequently brought on by the transfer or dispersal of entire organisms or entire genomes from one group to another. Immigrant genomes may be absorbed into a new population by sexual reproduction or hybridization, and they will progressively be broken apart through recombination. Therefore, “genotype flow” would be a more appropriate name to describe the simultaneous movement of the entire genome. The word “gene flow” is used, although it does not imply that genes are transmitted one at a time, likely due to an implicit assumption in abundant recombination and the fact that most theory is still based on straightforward single locus models. The fact that genotype flow typically drives gene flow has significant ramifications for how it is measured.
Key points to be remembered!
1. GP1 is the most often used gene pool in breeding programs.
2. Gradual decline in viability between their wild and cultivated forms: Genetic Divorce
3. A significant number of crop species’ lines, varieties, and related wild species make up a collection of crop species’ germplasm known as Bank Gene
4. Seeds that are 100% fertile and made from the first gene pool (GP1)
5. Seeds that were partially viable after being crossed with GP1: additional gene pool (GP2)
6. High hybridization difficulty and sterile hybrids when crossing with GP1 Tertiary gene pool is the name of (GP3)
7. GP-4 also known as Gene-ocean GP4 is connected to the “Trans gene”