Panmixia
Encyclopedia
Panmixia means random mating.
A panmictic population is one where all individuals are potential partners. This assumes that there are no mating restrictions, neither genetic
or behavioural, upon the population, and that therefore all recombination is possible. The Wahlund effect
assumes that the overall population is panmictic.
In genetics
, random mating involves the mating
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
and is distinct from lack of natural selection
: in viability selection for instance, selection occurs before mating.
to move about freely within their habitat
, possibly over a range of hundreds to thousands of miles, and thus breed with other members of the population that defines panmixia (or panmicticism).
To signify the importance of this, imagine several different finite populations of the same species
(for example: a grazing herbivore
), isolated from each other by some physical characteristic of the environment (dense forest
areas separating grazing lands). As time progresses, natural selection
and genetic drift
will slowly move the species toward either separate speciation events or extirpation
.
However, if the separating factor is removed before this happens (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. As the species's populations interbreed over time, they become more uniform, with a decrease in genetic diversity
, and thus a decrease in total biodiversity
.
In attempting to describe the mathematical properties of structured populations, Sewall Wright
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.
A panmictic population is one where all individuals are potential partners. This assumes that there are no mating restrictions, neither genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
or behavioural, upon the population, and that therefore all recombination is possible. The Wahlund effect
Wahlund effect
In population genetics, the Wahlund effect refers to reduction of heterozygosity in a population caused by subpopulation structure. Namely, if two or more subpopulations have different allele frequencies then the overall heterozygosity is reduced, even if the subpopulations themselves are in a...
assumes that the overall population is panmictic.
In genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
, random mating involves the mating
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
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
Hardy-Weinberg principle
The Hardy–Weinberg principle states that both allele and genotype frequencies in a population remain constant—that is, they are in equilibrium—from generation to generation unless specific disturbing influences are introduced...
and is distinct from lack of natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
: in viability selection for instance, selection occurs before mating.
Description
In simpler terms, it is the ability of individuals in a populationPopulation
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
to move about freely within their habitat
Habitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...
, possibly over a range of hundreds to thousands of miles, and thus breed with other members of the population that defines panmixia (or panmicticism).
To signify the importance of this, imagine several different finite populations of the same species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
(for example: a grazing herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
), isolated from each other by some physical characteristic of the environment (dense forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
areas separating grazing lands). As time progresses, natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
and genetic drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
will slowly move the species toward either separate speciation events or extirpation
Local extinction
Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...
.
However, if the separating factor is removed before this happens (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. As the species's populations interbreed over time, they become more uniform, with a decrease in genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
, and thus a decrease in total biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
.
In attempting to describe the mathematical properties of structured populations, Sewall Wright
Sewall Wright
Sewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...
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.