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Panmixia (or panmixis) means random mating. A panmictic population is one where all individuals are potential partners. This assumes that there are no mating restrictions, neither genetic nor
behavioural Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...
, upon the population and that therefore all recombination is possible. The
Wahlund effect In population genetics, the Wahlund effect is a reduction of heterozygosity (that is when an organism has two different alleles at a locus) in a population caused by subpopulation structure. Namely, if two or more subpopulations are in a Hardy– ...
assumes that the overall population is panmictic. In
genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...
, random mating involves the
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 reprod ...
of individuals regardless of any physical, genetic or social preference. In other words, the mating between two organisms is not influenced by any environmental, hereditary or social interaction. Hence, potential mates have an equal chance of being selected. Random mating is a factor assumed in the
Hardy–Weinberg principle In population genetics, the Hardy–Weinberg principle, also known as the Hardy–Weinberg equilibrium, model, theorem, or law, states that allele and genotype frequencies in a population will remain constant from generation to generation in t ...
and is distinct from lack of
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. Cha ...
: in viability selection for instance, selection occurs ''before'' mating.


Description

In simple terms, panmixia (or panmicticism) is the ability of individuals in 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 a ...
to interbreed without restrictions; individuals are able to move about freely within their
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 ...
, possibly over a range of hundreds to thousands of miles, and thus breed with other members of the population. To signify the importance of this, imagine several different finite populations of the same
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 s ...
(for example: a grazing herbivore), isolated from each other by some physical characteristic of the environment (dense
forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...
areas separating grazing lands). As time progresses,
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. Cha ...
and
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 ...
will slowly move each population toward genetic differentiation that would make each population genetically unique (that could eventually lead to speciation events or
extirpation Local extinction, also known as extirpation, refers to a species (or other taxon) of plant or animal that ceases to exist in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinct ...
). However, if the separating factor is removed before this happens (e.g. a road is cut through the forest), and the individuals are allowed to move about freely, the individual populations will still be able to
interbreed In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in ...
. As the species's populations interbreed over time, they become more genetically uniform, functioning again as a single panmictic population. In attempting to describe the mathematical properties of structured populations,
Sewall Wright Sewall Green Wright FRS(For) Honorary FRSE (December 21, 1889March 3, 1988) was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. He was a founder of population genetics alongsi ...
proposed a "factor of Panmixia" (P) to include in the equations describing the gene frequencies in a population, and accounting for a population's tendency towards panmixia, while a "factor of Fixation" (F) would account for a population's departure from the Hardy–Weinberg expectation, due to less than panmictic mating. In this formulation, the two quantities are complementary, i.e. ''P'' = 1 − ''F''. From this factor of fixation, he later developed the
F statistics In population genetics, ''F''-statistics (also known as fixation indices) describe the statistically expected level of Zygosity, heterozygosity in a population; more specifically the expected degree of (usually) a reduction in heterozygosity when ...
.


Background information

In a panmictic species, all of the individuals of a single species are potential partners, and the species gives no mating restrictions throughout the population. Panmixia can also be referred to as random mating, referring to a population that randomly chooses their mate, rather than sorting between the adults of the population. Panmixia allows for species to reach genetic diversity through gene flow more efficiently than monandry species. However, outside population factors, like drought and limited food sources, can affect the way any species will mate. When scientists examine species mating to understand their mating style, they look at factors like genetic markers, genetic differentiation, and gene pool.


Panmictic species

A panmictic population of ''
Monostroma ''Monostroma'' is a genus of marine green algae (seaweed) in the family Monostromataceae. As the name suggests, algae of this genus are monostromatic (single cell layered). ''Monostroma kuroshiense'', an algae of this genus, is commercially culti ...
latissimum'', a marine green algae, shows sympatric speciation in southwest Japanese islands. Although panmictic, the population is diversifying. Dawson's Burrowing bee, ''Amegilla dawsoni,'' may be forced to aggregate in common mating areas due to uneven resource distribution in its harsh desert environment. ''
Pantala flavescens ''Pantala flavescens'', the globe skimmer, globe wanderer or wandering glider, is a wide-ranging dragonfly of the family Libellulidae. This species and ''Pantala hymenaea'', the "spot-winged glider", are the only members of the genus ''Pantala ...
'' should be considered as a global panmictic population.


Related experiments and species

# ''Anguilla rostrate,'' or the American eel, exhibits panmixia throughout the entire species. This allows the eel to have phenotypic variation in their offspring and survive in a wide range of environmental conditions # In 2016, BMC Evolutionary Biology conducted a study on ''Pachygrapsus marmoratus'', the marbled crab, marking them as panmictic species. The study claimed that the crabs' mating behavior is characterized by genetic differentiation due to geographic breaks across its distribution range and not panmixia # In a heterogeneous environment such as the forests of Oregon, United States, Douglas squirrels (''Tamiasciurus douglasii'') exhibit local patterns of adaptation. In a study conducted by Chaves (2014) a population along an entire transect was found to be panmictic. Traits observed in this study included skull shape, fur color, etc. # Swordfish based in the Indian Ocean (''Xiphias gladius'') have been found to be a single panmictic population. Markers used in the study carried out by Muths et al (2013) found large spatial and temporal homogeneity in genetic structure satisfactory in order to consider the swordfish a singular panmictic population.


See also

*
Assortative mating Assortative mating (also referred to as positive assortative mating or homogamy) is a mating pattern and a form of sexual selection in which individuals with similar phenotypes or genotypes mate with one another more frequently than would be ex ...
(one form of non-random mating) *
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 (biology), adaptation, ...
*
Monogamy Monogamy ( ) is a form of dyadic relationship in which an individual has only one partner during their lifetime. Alternately, only one partner at any one time (serial monogamy) — as compared to the various forms of non-monogamy (e.g., polyg ...
: A mating system in which one male mates with just one female, and one female mates with just one male, in breeding season * Polygyny: A mating system in which a male fertilizes the eggs of several partners in breeding season *
Sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex ( ...
: A form of natural selection that occurs when individuals vary in their ability to compete with others for mates or to attract members of the opposite sex * Fitness: A measure of the genes contributed to the next generation by an individual, often stated in terms of the number of surviving offspring produced by the individual


References


Further reading

* * {{cite journal , last1=Chavez, A. S., & Kenagy, G. J. , author-link=Jim Kenagy , title=Clinal colour variation within a panmictic population of tree squirrels, Tamiasciurus douglasii ( Rodentia: Sciuridae), across an ecological gradient , journal=Biological Journal of the Linnean Society , date=2014 , volume=113 , issue=2 , page=536 , doi=10.1111/bij.12361 , doi-access=free Population Population genetics