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Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate ...
and can be attributed to the span of survival for a species. It is distinguished from ''
genetic variability Genetic variability is either the presence of, or the generation of, genetic differences. It is defined as "the formation of individuals differing in genotype, or the presence of genotypically different individuals, in contrast to environmentally i ...
'', which describes the tendency of genetic characteristics to vary. Genetic diversity serves as a way for populations to adapt to changing environments. With more variation, it is more likely that some individuals in a population will possess variations of
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
s that are suited for the environment. Those individuals are more likely to survive to produce offspring bearing that allele. The population will continue for more generations because of the success of these individuals. The academic field of
population genetics Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and p ...
includes several hypotheses and theories regarding genetic diversity. The neutral theory of evolution proposes that diversity is the result of the accumulation of neutral substitutions. Diversifying selection is the hypothesis that two subpopulations of a species live in different environments that select for different alleles at a particular locus. This may occur, for instance, if a species has a large range relative to the mobility of individuals within it.
Frequency-dependent selection Frequency-dependent selection is an evolutionary process by which the fitness of a phenotype or genotype depends on the phenotype or genotype composition of a given population. * In positive frequency-dependent selection, the fitness of a phenotyp ...
is the hypothesis that as alleles become more common, they become more vulnerable. This occurs in host–pathogen interactions, where a high frequency of a defensive allele among the
host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People * Jim Host (born 1937), American businessman * Michel Hos ...
means that it is more likely that a
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ge ...
will spread if it is able to overcome that
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
.


Within species diversity

A study conducted by the
National Science Foundation The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the Natio ...
in 2007 found that genetic diversity (within
species diversity Species diversity is the number of different species that are represented in a given community (a dataset). The effective number of species refers to the number of equally abundant species needed to obtain the same mean proportional species abunda ...
) and
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species (''species diversity''), and ecosystem ('' ecosystem diversity'') ...
are dependent upon each other — i.e. that diversity within a species is necessary to maintain diversity among species, and vice versa. According to the lead researcher in the study, Dr. Richard Lankau, "If any one type is removed from the system, the cycle can break down, and the community becomes dominated by a single species."
Genotypic The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
and
phenotypic In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological prop ...
diversity have been found in all species at the
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
, DNA, and
organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...
al levels; in nature, this diversity is nonrandom, heavily structured, and correlated with environmental variation and stress. The interdependence between genetic and species diversity is delicate. Changes in species diversity lead to changes in the environment, leading to adaptation of the remaining species. Changes in genetic diversity, such as in loss of species, leads to a loss of
biological diversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species (''species diversity''), and ecosystem ('' ecosystem diversity'') ...
. Loss of genetic diversity in domestic animal populations has also been studied and attributed to the extension of markets and
economic globalization Economic globalization is one of the three main dimensions of globalization commonly found in academic literature, with the two others being political globalization and cultural globalization, as well as the general term of globalization. Eco ...
.


Evolutionary importance of genetic diversity


Adaptation

Variation in the populations gene pool allows
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charl ...
to act upon traits that allow the population to adapt to changing environments. Selection for or against a trait can occur with changing environment – resulting in an increase in genetic diversity (if a new
mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...
is selected for and maintained) or a decrease in genetic diversity (if a disadvantageous allele is selected against). Hence, genetic diversity plays an important role in the survival and adaptability of a species. The capability of the population to adapt to the changing environment will depend on the presence of the necessary genetic diversity The more genetic diversity a population has, the more likelihood the population will be able to adapt and survive. Conversely, the vulnerability of a population to changes, such as climate change or novel
disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that ...
s will increase with reduction in genetic diversity. For example, the inability of koalas to adapt to fight
Chlamydia Chlamydia, or more specifically a chlamydia infection, is a sexually transmitted infection caused by the bacterium '' Chlamydia trachomatis''. Most people who are infected have no symptoms. When symptoms do appear they may occur only several we ...
and the
koala retrovirus ''Koala retrovirus'' (KoRV) is a retrovirus that is present in many populations of koalas. It has been implicated as the agent of koala immune deficiency syndrome (KIDS), an AIDS-like immunodeficiency that leaves infected koalas more susceptible ...
(KoRV) has been linked to the koala's low genetic diversity. This low genetic diversity also has geneticists concerned for the koalas' ability to adapt to climate change and human-induced environmental changes in the future.


Small populations

Large populations are more likely to maintain genetic material and thus generally have higher genetic diversity. Small populations are more likely to experience the loss of diversity over time by random chance, which is called
genetic drift Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene variants to disappear completely and there ...
. When an
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
(variant of a gene) drifts to fixation, the other allele at the same locus is lost, resulting in a loss in genetic diversity. In small population sizes,
inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and ...
, or
mating In biology, mating is the pairing of either opposite- sex or hermaphroditic organisms for the purposes of sexual reproduction. '' Fertilization'' is the fusion of two gametes. '' Copulation'' is the union of the sex organs of two sexually r ...
between individuals with similar genetic makeup, is more likely to occur, thus perpetuating more common alleles to the point of fixation, thus decreasing genetic diversity. Concerns about genetic diversity are therefore especially important with large mammals due to their small population size and high levels of human-caused population effects. 6/sup> A genetic bottleneck can occur when a population goes through a period of low number of individuals, resulting in a rapid decrease in genetic diversity. Even with an increase in population size, the genetic diversity often continues to be low if the entire species began with a small population, since beneficial mutations (see below) are rare, and the gene pool is limited by the small starting population. This is an important consideration in the area of
conservation genetics Conservation genetics is an interdisciplinary subfield of population genetics that aims to understand the dynamics of genes in populations principally to avoid extinction. Therefore, it applies genetic methods to the conservation and restoratio ...
, when working toward a rescued population or species that is genetically-healthy.


Mutation

Random
mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...
s consistently generate
genetic variation Genetic variation is the difference in DNA among individuals or the differences between populations. The multiple sources of genetic variation include mutation and genetic recombination. Mutations are the ultimate sources of genetic variation, ...
. A mutation will increase genetic diversity in the short term, as a new gene is introduced to the gene pool. However, the persistence of this gene is dependent of drift and selection (see above). Most new mutations either have a neutral or negative effect on fitness, while some have a positive effect. A beneficial mutation is more likely to persist and thus have a long-term positive effect on genetic diversity. Mutation rates differ across the genome, and larger populations have greater mutation rates. In smaller populations a mutation is less likely to persist because it is more likely to be eliminated by drift.


Gene flow

Gene flow In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent a ...
, often by migration, is the movement of genetic material (for example by pollen in the wind, or the migration of a bird). Gene flow can introduce novel alleles to a population. These alleles can be integrated into the population, thus increasing genetic diversity. For example, an
insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed t ...
-resistant mutation arose in '' Anopheles gambiae'' African mosquitoes. Migration of some ''A. gambiae'' mosquitoes to a population of '' Anopheles coluzziin'' mosquitoes resulted in a transfer of the beneficial resistance gene from one species to the other. The genetic diversity was increased in ''A. gambiae'' by mutation and in ''A. coluzziin'' by gene flow.


In agriculture


In crops

When humans initially started farming, they used
selective breeding Selective breeding (also called artificial selection) is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant ma ...
to pass on desirable traits of the crops while omitting the undesirable ones. Selective breeding leads to
monoculture In agriculture, monoculture is the practice of growing one crop species in a field at a time. Monoculture is widely used in intensive farming and in organic farming: both a 1,000-hectare/acre cornfield and a 10-ha/acre field of organic kale are ...
s: entire farms of nearly genetically identical plants. Little to no genetic diversity makes crops extremely susceptible to widespread disease; bacteria morph and change constantly and when a disease-causing bacterium changes to attack a specific genetic variation, it can easily wipe out vast quantities of the species. If the genetic variation that the bacterium is best at attacking happens to be that which humans have selectively bred to use for harvest, the entire crop will be wiped out. The nineteenth-century Great Famine in Ireland was caused in part by a lack of biodiversity. Since new potato plants do not come as a result of reproduction, but rather from pieces of the parent plant, no genetic diversity is developed, and the entire crop is essentially a clone of one potato, it is especially susceptible to an epidemic. In the 1840s, much of Ireland's population depended on potatoes for food. They planted namely the "lumper" variety of potato, which was susceptible to a rot-causing
oomycete Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the res ...
called ''
Phytophthora infestans ''Phytophthora infestans'' is an oomycete or water mold, a fungus-like microorganism that causes the serious potato and tomato disease known as late blight or potato blight. Early blight, caused by '' Alternaria solani'', is also often called ...
''. The fungus destroyed the vast majority of the potato crop, and left one million people to starve to death. Genetic diversity in agriculture does not only relate to disease, but also
herbivores A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthp ...
. Similarly, to the above example, monoculture agriculture selects for traits that are uniform throughout the plot. If this
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
is susceptible to certain herbivores, this could result in the loss of a large portion of the crop. One way farmers get around this is through inter-cropping. By planting rows of unrelated, or genetically distinct crops as barriers between herbivores and their preferred host plant, the farmer effectively reduces the ability of the herbivore to spread throughout the entire plot.


In livestock

The genetic diversity of livestock species permits
animal husbandry Animal husbandry is the branch of agriculture concerned with animals that are raised for meat, fibre, milk, or other products. It includes day-to-day care, selective breeding, and the raising of livestock. Husbandry has a long history, start ...
in a range of environments and with a range of different objectives. It provides the raw material for
selective breeding Selective breeding (also called artificial selection) is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant ma ...
programmes and allows livestock populations to adapt as environmental conditions change. Livestock biodiversity can be lost as a result of
breed A breed is a specific group of domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same species. In literature, there exist several slig ...
extinctions and other forms of
genetic erosion Genetic erosion (also known as genetic depletion) is a process where the limited gene pool of an endangered species diminishes even more when reproductive individuals die off before reproducing with others in their endangered low population. The ...
. As of June 2014, among the 8,774 breeds recorded in the Domestic Animal Diversity Information System (
DAD-IS DAD-IS is the acronym of the worldwide Domestic Animal Diversity Information System of the Food and Agriculture Organization of the United Nations, within the FAO's management of animal genetic resources programme.Domestic Animal Diversity Info ...
), operated by the Food and Agriculture Organization of the United Nations ( FAO), 17 percent were classified as being at risk of extinction and 7 percent already extinct. There is now a Global Plan of Action for Animal Genetic Resources that was developed under the auspices of the Commission on Genetic Resources for Food and Agriculture in 2007, that provides a framework and guidelines for the management of animal genetic resources. Awareness of the importance of maintaining animal genetic resources has increased over time. FAO has published two reports on the state of the world's animal genetic resources for food and agriculture, which cover detailed analyses of our global livestock diversity and ability to manage and conserve them.


Viral implications

High genetic diversity in viruses must be considered when designing vaccinations. High genetic diversity results in difficulty in designing targeted vaccines, and allows for viruses to quickly evolve to resist vaccination lethality. For example, malaria vaccinations are impacted by high levels of genetic diversity in the protein antigens. In addition,
HIV-1 The subtypes of HIV include two major types, HIV type 1 (HIV-1) and HIV type 2 (HIV-2). HIV-1 is related to viruses found in chimpanzees and gorillas living in western Africa, while HIV-2 viruses are related to viruses found in the sooty manga ...
genetic diversity limits the use of currently available viral load and resistance tests.


Coping with low genetic diversity


Natural

The natural world has several ways of preserving or increasing genetic diversity. Among oceanic
plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cr ...
,
virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovs ...
es aid in the genetic shifting process. Ocean viruses, which infect the plankton, carry genes of other organisms in addition to their own. When a virus containing the genes of one cell infects another, the genetic makeup of the latter changes. This constant shift of genetic makeup helps to maintain a healthy population of plankton despite complex and unpredictable environmental changes.
Cheetah The cheetah (''Acinonyx jubatus'') is a large cat native to Africa and central Iran. It is the fastest land animal, estimated to be capable of running at with the fastest reliably recorded speeds being , and as such has evolved specialize ...
s are a
threatened species Threatened species are any species (including animals, plants and fungi) which are vulnerable to endangerment in the near future. Species that are threatened are sometimes characterised by the population dynamics measure of '' critical depe ...
. Low genetic diversity and resulting poor sperm quality has made breeding and survivorship difficult for cheetahs. Moreover, only about 5% of cheetahs survive to adulthood However, it has been recently discovered that female cheetahs can mate with more than one male per litter of cubs. They undergo induced ovulation, which means that a new egg is produced every time a female mates. By mating with multiple males, the mother increases the genetic diversity within a single litter of cubs.


Human intervention

Attempts to increase the viability of a species by increasing genetic diversity is called genetic rescue. For example, eight panthers from
Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
were introduced to the
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
panther population, which was declining and suffering from inbreeding depression. Genetic variation was thus increased and resulted in a significant increase in population growth of the Florida Panther. Creating or maintaining high genetic diversity is an important consideration in species rescue efforts, in order to ensure the longevity of a population.


Measures

Genetic diversity of a population can be assessed by some simple measures. *Gene diversity is the proportion of polymorphic loci across the
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
. *
Heterozygosity Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...
is the fraction of individuals in a population that are heterozygous for a particular locus. *Alleles per locus is also used to demonstrate variability. * Nucleotide diversity is the extent of nucleotide polymorphisms within a population, and is commonly measured through molecular markers such as micro- and minisatellite sequences, mitochondrial DNA, and
single-nucleotide polymorphism In genetics, a single-nucleotide polymorphism (SNP ; plural SNPs ) is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently ...
s (SNPs). Furthermore, stochastic simulation software is commonly used to predict the future of a population given measures such as allele frequency and population size. Genetic diversity can also be measured.The various recorded ways of measuring genetic diversity include: *
Species richness Species richness is the number of different species represented in an ecological community, landscape or region. Species richness is simply a count of species, and it does not take into account the abundances of the species or their relative a ...
is a measure of the number of species * Species abundance a relative measure of the abundance of species * Species density an evaluation of the total number of species per unit area


See also

*
Biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species (''species diversity''), and ecosystem ('' ecosystem diversity'') ...
*
Center of diversity A center of origin is a geographical area where a group of organisms, either domesticated or wild, first developed its distinctive properties. They are also considered centers of diversity. Centers of origin were first identified in 1924 by N ...
*
Genetic variation Genetic variation is the difference in DNA among individuals or the differences between populations. The multiple sources of genetic variation include mutation and genetic recombination. Mutations are the ultimate sources of genetic variation, ...
* Genetic resources *
Human genetic variation Human genetic variation is the genetic differences in and among populations. There may be multiple variants of any given gene in the human population (alleles), a situation called polymorphism. No two humans are genetically identical. Even ...
* Human Variome Project *
International HapMap Project The International HapMap Project was an organization that aimed to develop a haplotype map (HapMap) of the human genome, to describe the common patterns of human genetic variation. HapMap is used to find genetic variants affecting health, disease ...


References


External links


Implementing the Global Plan of Action on Animal Genetic Resources

Domestic Animal Diversity Information System

Commission on Genetic Resources for Food and Agriculture
{{DEFAULTSORT:Genetic Diversity Biodiversity Genetics concepts Population genetics