Genetic viability is the ability of the genes present to allow a cell, organism or population to survive and reproduce. The term is generally used to mean the chance or ability of a

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using ...

to avoid the problems of

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 an ...

. Less commonly genetic viability can also be used in respect to a single cell or on an individual level. Inbreeding depletes

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 ...

of the genome, meaning there is a greater chance of identical alleles at a locus. When these alleles are non-beneficial, homozygosity could cause problems for genetic viability. These problems could include effects on the individual fitness (higher mortality, slower growth, more frequent developmental defects, reduced mating ability, lower fecundity, greater susceptibility to disease, lowered ability to withstand stress, reduced intra- and inter-specific competitive ability) or effects on the entire population fitness (depressed population growth rate, reduced regrowth ability, reduced ability to adapt to environmental change). See

Inbreeding depression Inbreeding depression is the reduced biological fitness which has the potential to result from inbreeding (the breeding of related individuals). Biological fitness refers to an organism's ability to survive and perpetuate its genetic material. ...

. When a population of plants or animals loses their genetic viability, their chance of going extinct increases.

Necessary conditions

To be genetically viable, a population of plants or animals requires a certain amount of

genetic diversity Genetic diversity is the total number of Genetics, genetic characteristics in the genetic makeup of a species, it ranges widely from the number of species to differences within species and can be attributed to the span of survival for a species. ...

and a certain

population size In population genetics and population ecology, population size (usually denoted ''N'') is the number of individual organisms in a population. Population size is directly associated with amount of genetic drift, and is the underlying cause of effect ...

. For long-term genetic viability, the population size should consist of enough breeding pairs to maintain genetic diversity. The precise

effective population size The effective population size (''N'e'') is a number that, in some simplified scenarios, corresponds to the number of breeding individuals in the population. More generally, ''N'e'' is the number of individuals that an idealised population w ...

can be calculated using a

minimum viable population Minimum viable population (MVP) is a lower bound on the population of a species, such that it can survive in the wild. This term is commonly used in the fields of biology, ecology, and conservation biology Conservation biology is the study of ...

analysis. Higher genetic diversity and a larger population size will decrease the negative effects of

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 ...

and inbreeding in a population. When adequate measures have been met, the genetic viability of a population will increase.

Causes for decrease

The main cause of a decrease in genetic viability is loss of

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

. This loss can occur because of, for example

urbanization Urbanization (or urbanisation) refers to the population shift from rural to urban areas, the corresponding decrease in the proportion of people living in rural areas, and the ways in which societies adapt to this change. It is predominantly t ...

or deforestation causing

habitat fragmentation Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological proces ...

. Natural events like earthquakes, floods or fires can also cause loss of habitat. Eventually, loss of habitat could lead to a

population bottleneck A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Go ...

. In a small population, the risk of inbreeding will increase drastically which could lead to a decrease in genetic viability. If they are specific in their diets, this can also lead to habitat isolation and reproductive constraints, leading to greater population bottleneck, and decrease in genetic viability. Traditional artificial propagation can also lead to decreases in genetic viability in some species.

Population conservation

Habitat protection is associated with more allelic richness and heterozygosity than in unprotected habitats. Reduced habitat fragmentation and increased landscape permeability can promote allelic richness by facilitating gene flow between populations that are isolated or smaller. The minimum viable population needed to maintain genetic viability is where the loss of genetic variation because of small population size (

) is equal to genetic variation gained through

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, m ...

. When the numbers of one sex is too low, there may be a need for crossbreeding to maintain viability.

Analyzing

When genetic viability seems to be decreasing within a population, a

population viability analysis Population viability analysis (PVA) is a species-specific method of risk assessment frequently used in conservation biology. It is traditionally defined as the process that determines the probability that a population will go extinct within a given ...

(PVA) can be done to assess the risk of extinction of this species. The result of a PVA could determine whether further action is needed regarding the preservation of a species.

Applications

Genetic viability is applied by wildlife management staff in zoos, aquariums or other such ex situ habitats. They use the knowledge of the animals' genetics, usually through their pedigrees, to calculate the PVA and manage the population viability.

References

Genetics {{genetics-stub