Gene Pool- Definition, Working, Types, Evolution, Examples

Gene pool refers to the collection of the total genes or genetic makeup that can be transferred in the population of a single species from parent to offspring.

  • The Gene pool gives us information on the total genetic makeup of an entire population.
  • Alleles are also included in the gene pool. The composition of a gene pool in the population can change over time via evolution. Mutation, natural selection, and genetic drift are causes of change that occur in the gene pool.
  • Changes in a gene pool composition are essential for the survival of any population of species with the change in an environment.
  • There will be a higher gene pool if there is greater variation in a population.
  • The phenotypes which are present in the population at any time are determined by the gene pool.
  • The concept of a gene pool was proposed by Harlan and De Wet in 1971. The Russian Geneticist Alexander Sergeevich Serebrousky formulated the concept of the gene pool, who coined the term ‘genofond’, the English translation of which is the gene pool. 
  • A gene pool of a population describes as, genes present in the population, and proportions of different kinds of the gene in the individuals of the population.
  •  A large gene pool increases extensive genetic diversity within a population, passed to the next generations, while a small gene pool represents a lower genetic diversity within a population and becomes extinct.
Gene Pool
Gene Pool

How do Gene Pools works?

  • The Gene pool of the species changes over time. When a mutation occurs gene pool increases but when the allele dies out gene pool decreases. Gene pools ensure genetic diversity within the population.
  • Within the gene pool, beneficial adaptations become more frequent, and the less desirable characteristics become less prevalent or may even vanish entirely from the gene pool.
  • Let’s take the example of the fruit fly. Out of 1000 populations, 20 different alleles is present in locus 1. If we select only five individuals, we can find only three different alleles at locus 1.
  • If we bread these flies to make them 1000, the gene pool shrinks and becomes much smaller than the original one.
  • This occurs when species are under extinction. As a result of the low gene pool, there is also low variation. If harmful alleles survive during shrinkage of the gene pool, it causes genetic problems like low fertility, deformity, and diseases. For example, it occurs in animal breeding and animal near extinction. Outbreeding helps to increase the gene pool and resistance to genetic problems.

Types of the Gene Pool 

According to Harlan and de Wet Classification (1971), the gene pool of crop breeding is divided into three types based on the degree of relationship. They are the primary gene pool, secondary gene pool, and tertiary gene pool.

1. Primary gene pool (GP1): 

  • Members of the primary gene pool include the same species or closely related species which produce completely fertile offspring on inter-mating.
  • Crossing between a member of GP1 is very easy. The resulting hybrids are vigorous and show normal meiotic chromosome pairing and recombination.
  • There is normal gene segregation, and seed fertility is complete.
  • Members of this group are the most commonly used in breeding programs.     

2. Secondary gene pool (GP2):

  • The secondary gene pool includes all those species that hybridize with those of the primary gene pool with some to considerable difficulty, and the hybrid is at least partially fertile,
  • The difficulty in hybridization is due to ploidy differences, chromosome alternations, or genetic barriers.
  • Members of this group are often used in breeding programs.
  • There is some reproductive barrier between members of the secondary gene pool and primary gene pool, which leads to partial sterile and weak hybrid, chromosomes may pair poorly or not at all, difficulty in recover of desire phenotype in subsequent generations, and efforts are required for available gene pool utilized by plant breeder or geneticist.

3. Tertiary gene pool (GP3):

  • Members of tertiary gene pools cross with the members of the primary gene pool with consideration to great difficulty, and hybrids, if produced, are anomalous, lethal, or completely sterile.
  • To exploit germplasm from distant relatives, tools such as embryo rescue and bridge crossing may be used to nurture an embryo from a wide cross to a full plant and to obtain fertile plants.
  • Used only occasionally in breeding programs.
  • Gene transfer from GP3 to GP2 is relatively easier.
  • The primary and tertiary gene pools can be intermated, but without any special technique (such as embryo rescue, induced polyploidy, and, bridging crosses), gene transfer between them is impossible. 
  • Some crop plants have no secondary gene pools. Some examples are barley, soybean, onion, and broad bean.  

 Gene Pool Evolution

  • Evolution is a change in allele frequency. Allele frequency and gene pool change by mutation, gene flow, genetic drifts, and natural selection.
  • Natural selection pressure (predation, disease, competition) creates difficulty in survival, and the ones who survive are those best adapted. These individuals have beneficial alleles which pass to the next generation. As a result, a higher amount of beneficial alleles transfer into the next generation and contribute to the change in the gene pool.
  • The population evolutionary trajectory is directly affected by the size of the gene pool. The gene pool gets expands when new people immigrate into the population with special features or shrinks when emigrating from the population.
  • The various adaptation takes place within the gene pool where beneficial adaptation becomes more frequent and non-beneficial adaptation became less prevalent or may completely disappear from the gene pool.
  • With the change in local climate, there is more likely to survive in such dynamic conditions.
  • The population with a larger gene pool than the population with a smaller gene pool.
  • The mutation causes a permanent change of genes that leads to variation in the next generation due to a new set of genes. 
  • Hybridization involves the introduction of genes from an outside source through inbreeding, altering the existing gene pool.
  • Recombination occurs during meiosis and leads to the formation of new genotypes or changes in the gene pool from the already existing genes either by crossing over or assortment/separation of chromosomes.
  • Speciation is observed when small changes to an allelic frequency are called microevolution and large changes, or an accumulation of small changes called macroevolution occurs.
  • Example: Individuals who are antibiotic-resistant bacteria can resist any type of intervention, classification of the plant as a weed is the result of its diverse gene pool and can survive in any environment, advanced hybrids have a very small gene pool that has specific features, and dandelions have a large size gene pool so prefer hybrid roses.

Examples of Gene pool

Gene pool in Humans

  • Within one DNA, the human gene pool consists of every allele variant of approximately 19,000-20,000. Like every human being, human genes can interbreed with each other as a single species.
  • For example, skin pigmentation occurred when the human population migrated to the northern hemisphere from the equatorial region. The skin color of the human population changed into lighter color from the existing color due to the exposure to low sunlight for the increment of the absorption process of Vitamin D. Such type of genetic modification becomes part of the human gene pool in that particular region. 

Gene pool in Butterflies

  • In the population of butterflies, if they have eyespots on their wings, then they contain a dominant allele, whereas if they don’t have such eyespots on wings, then they are homozygous (i.e., having two of the same copies) for the recessive allele.

References

  1. https://www.vedantu.com/biology/gene-pool.
  2. https://biologydictionary.net/gene-pool.
  3. https://study.com/learn/lesson/gene-pool-concept-examples.html
  4. https://www.onlinebiologynotes.com/genetic-variation-as-a-cause-of-evolution.
  5. https://www.britannica.com/science/gene-pool.
  6. https://agriinfo.in/the-gene-pool-system-of-classification-2071

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