Variety in Characteristics

Populations can adapt to changing surroundings thanks to genetic variety. With more variation, it’s more possible that certain people in a group will have alleles that are better suited to their surroundings. Those people are more likely to live long enough to have offspring with that allele. Because of their success, the population will continue for many more generations. 

Several hypotheses and theories about genetic diversity can be found in the academic discipline of population genetics. According to the neutral theory of evolution, variety arises from the accumulation of neutral replacements. Diversifying selection is the idea that two subpopulations of a species exist in distinct environments and choose different alleles at the same locus. This could happen, for example, if a species’ range is enormous in comparison to its individual mobility. The concept behind frequency-dependent selection is that as alleles get more common, they become more vulnerable. This happens in host–pathogen interactions, where a pathogen with a high frequency of a defensive allele among the host is more likely to propagate if it can overcome that allele.

Within species diversity

Maize varieties in Russian plant scientist Nikolai Vavilov’s office

A 2007 National Science Foundation study concluded that genetic variety (within species diversity) and biodiversity are interdependent; diversity within a species is needed to preserve biodiversity between species, and vice versa. “If any type is removed from the system, the cycle might break down and the community becomes dominated by a single species,” says study author Dr. Richard Lankau. Genotypic and phenotypic diversity exist at the protein, DNA, and organismal levels in all organisms. In nature, this diversity is nonrandom, substantially organised, and connected with environmental variation and stress.

Genetic and species diversity are interdependent. Changes in species diversity affect the environment, causing remaining species to adapt. Species extinctions and genetic changes lead to a loss of biological diversity. The loss of genetic diversity in domestic animal populations has also been linked to commercial expansion and globalisation.

Evolutionary importance of genetic diversity

Adaptation

Natural selection can act on features that allow a population to adapt to changing circumstances because of genetic variation. Changes in the environment can result in selection for or against a trait, increasing or decreasing genetic diversity (if a novel mutation is selected for and sustained) (if a disadvantageous allele is selected against). Genetic diversity helps a species survive and adapt. The population’s ability to adapt to changing conditions is dependent on genetic variety. More genetic variety increases a population’s adaptability and survival. Reducing genetic variety increases a population’s vulnerability to climate change and new diseases. Low genetic variety may explain why koalas can’t fight Chlamydia and KoRV. Geneticists are concerned about the koalas’ ability to adapt to climate change and human-caused environmental changes.

Small populations

Large populations are more likely to keep genetic material, increasing genetic variety.

Genetic drift is the random loss of variety in small populations. When an allele fixes, the other allele at the same locus is lost, reducing genetic diversity. [13] Inbreeding, or mating between individuals with identical genetic composition, is more prevalent in small populations, diminishing genetic diversity and maintaining more common genes. [14] Because large mammals have tiny populations and high amounts of human-caused population effects, genetic diversity is a major concern.

A genetic bottleneck occurs when a population’s genetic variety rapidly decreases due to a lack of members. Even with a population growth, genetic diversity frequently remains low if the entire species began with a tiny population, since favourable mutations are rare and the gene pool is constrained by the small starting population. This is crucial in conservation genetics when trying to save a genetically healthy population or species.

Mutation

Mutations cause genetic diversity.

A mutation increases short-term genetic diversity by adding a new gene. This gene persists through drift and selection (see above). Some novel mutations improve fitness, but most do not. Beneficial mutations are more likely to persist and improve genetic diversity. Larger populations have higher mutation rates across the genome. In smaller populations, mutations are more likely to be eradicated via drift.

Gene flow

Migration causes gene flow (for example by pollen in the wind, or the migration of a bird). Gene flow can introduce new alleles. Their introduction into the population will increase genetic diversity.

Anopheles gambiae mosquitoes became insecticide resistant. The favourable resistance gene was transferred from one species to another when A. gambiae mosquitoes migrated to Anopheles coluzzii mosquitoes. Mutation and gene flow increased genetic diversity in A. gambiae and A. coluzzii.

In agriculture

Crops

Humans employed selective breeding to pass on favourable crop qualities while deleting unwanted ones. Selective breeding creates monocultures of almost identical plants. Little to no genetic diversity makes crops vulnerable to widespread illness; bacteria evolve and change constantly, and a disease-causing bacterium can swiftly wipe out enormous quantities of a species. If the bacterium’s preferred genetic variety happens to be the one humans have deliberately cultivated to employ for harvest, the crop is doomed.

Lack of biodiversity contributed to Ireland’s Great Famine in the 1800s. Since new potato plants do not arise from reproduction but from fragments of the parent plant, no genetic variety is created, and the entire crop is a clone of one potato, it is prone to an epidemic. In the 1840s, many Irish ate potatoes. “Lumper” potatoes were sensitive to Phytophthora infestans, a rot-causing oomycete. [19] The disease decimated the potato harvest, leaving one million people hungry.

Genetic diversity in agriculture affects herbivores and disease. Monoculture agriculture selects for plot-wide homogeneous features. If this genotype is sensitive to herbivores, the crop could be lost. Intercropping helps farmers avoid this. Planting rows of unrelated or genetically dissimilar crops between herbivores and their preferred host plant inhibits the herbivore’s capacity to spread across the entire plot.

In livestock

Genetic diversity allows animal husbandry in a variety of conditions and with diverse goals. It permits selective breeding programmes and animal herds to adapt to changing environmental conditions.

Breed extinctions and genetic degradation can reduce livestock biodiversity. 17 percent of the 8,774 breeds in the FAO’s Domestic Animal Diversity Information System (DAD-IS) were at risk of extinction in June 2014, and 7 percent were extinct. The Commission on Genetic Resources for Food and Agriculture developed a Global Plan of Action for Animal Genetic Resources in 2007, which provides a framework and principles for managing animal genetic resources.

Over time, awareness of animal genetic resources has grown. FAO has issued two assessments on the condition of the world’s animal genetic resources for food and agriculture, which analyse global livestock diversity and our ability to manage and conserve them.

Viral implications

Vaccines must consider viruses’ genetic diversity. High genetic variety makes targeting vaccines challenging and permits viruses to evolve to avoid vaccination lethality. For example, substantial genetic variation in protein antigens affects malaria vaccine. HIV-1 genetic diversity restricts viral load and resistance tests.

Measures

Simple measurements can assess a population’s genetic diversity.

• Gene diversity is the percentage of polymorphic genes

• Heterozygosity is the fraction of heterozygous individuals in a population

• Alleles per locus show variability

• Nucleotide diversity measures the extent of nucleotide polymorphisms in a population using molecular markers such as micro- and minisatellite sequences, mitochondrial DNA,and single-nucleotide polymorphisms (SNPs)

Stochastic simulation software is used to anticipate a population’s future based on allele frequency and population size.

Also measure genetic diversity.

Measurements of genetic diversity include:

• Number of species is species richness

• Relative species abundance

• Density is the number of species per unit area

Conclusion

In biology, a variation is any difference between cells, individual organisms, or groups of organisms of any species that is caused either by genetic differences (genotypic variation) or by the effect of environmental factors on the expression of the genetic potentials. Variation can be caused by genetic differences (genotypic variation) or by the effect of environmental factors on the expression of the genetic potentials (phenotypic variation).

Because of differences in their genes, certain members of a group of organisms are better equipped to endure the conditions of the environment in which they live than others. Even within a relatively small population, the degree to which individual organisms are optimised for survival in a particular setting might vary dramatically from one another.