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Encyclopedia > Population genetics

Population genetics is the study of the distribution of and change in allele frequencies under the influence of the four evolutionary forces: natural selection, genetic drift, mutation, and migration. It also takes account of population subdivision and population structure in space. As such, it attempts to explain such phenomena as adaptation and speciation. Population genetics was a vital ingredient in the modern evolutionary synthesis, its primary founders were Sewall Wright, J. B. S. Haldane and Ronald Fisher, who also laid the foundations for the related discipline of quantitative genetics. Allele frequency is a term of population genetics that is used in characterizing the genetic diversity of a species population, or equivalently the richness of its gene pool. ... Natural selection is the metaphor Charles Darwin used in 1859 to name the process he postulated to drive the adaptation of organisms to their environments and the origin of new species. ... Genetic drift is a contributing factor in biological evolution, in which traits which do not affect reproductive fitness change in a population over time. ... In biology, mutations are changes to the genetic material (usually DNA or RNA). ... This article is about non-human migration. ... The eye is an adaptation. ... Speciation refers to the evolutionary process by which new biological species arise. ... The modern evolutionary synthesis (often referred to simply as the modern synthesis or the evolutionary synthesis), neo-Darwinian synthesis or neo-Darwinism, generally denotes the combination of Charles Darwins theory of the evolution of species by natural selection, Gregor Mendels theory of genetics as the basis for biological... Sewall Green Wright (December 21, 1889– March 3, 1988) was an American geneticist known for his influential work on evolutionary theory. ... J.B.S. Haldane with his second wife Helen Spurway John Burdon Sanderson Haldane (November 5, 1892 – December 1, 1964), who normally used J.B.S. as a first name, was a British geneticist and evolutionary biologist. ... Sir Ronald Fisher Sir Ronald Aylmer Fisher, FRS (17 February 1890 – 29 July 1962) was a British eugenicist, evolutionary biologist, geneticist and statistician. ... Quantitative genetics is the study of continuous traits (such as height or weight) and its underlying mechanisms. ...

Contents


Scope and theoretical considerations

Perhaps the most significant "formal" achievement of the modern evolutionary synthesis has been the framework of mathematical population genetics. Indeed some authors (Beatty 1986) would argue that it defines the core of the modern synthesis. The modern evolutionary synthesis (often referred to simply as the modern synthesis or the evolutionary synthesis), neo-Darwinian synthesis or neo-Darwinism, generally denotes the combination of Charles Darwins theory of the evolution of species by natural selection, Gregor Mendels theory of genetics as the basis for biological...


Lewontin (1974) outlined the theoretical task for population genetics. He imagined two spaces: a "genotypic space" and a "phenotypic space". The challenge of a complete theory of population genetics is to provide a set of laws that predictably map a population of genotypes (G1) to a phenotype space (P1), where selection takes place, and another set of laws that map the resulting population (P2) back to genotype space (G2) where Mendelian genetics can predict the next generation of genotypes, thus completing the cycle. Even leaving aside for the moment the non-Mendelian aspects revealed by molecular genetics, this is clearly a gargantuan task. Visualizing this transformation: Richard Lewontin Richard Charles Dick Lewontin (born March 29, 1929) is an American evolutionary biologist, geneticist and social commentator. ... The genotype is the specific genetic makeup (the specific genome) of an individual, usually in the form of DNA. It codes for the phenotype of that individual. ... The phenotype of an individual organism is either its total physical appearance and constitution or a specific manifestation of a trait, such as size or eye color, that varies between individuals. ... Natural selection is the metaphor Charles Darwin used in 1859 to name the process he postulated to drive the adaptation of organisms to their environments and the origin of new species. ... Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets that underlie much of genetics developed by Gregor Mendel in the latter part of the 19th century. ... Molecular genetics is the field of biology which studies the structure and function of genes at a molecular level. ...

(adapted from Lewontin 1974, p. 12).


T1 represents the genetic and epigenetic laws, the aspects of functional biology, or development, that transform a genotype into phenotype. We will refer to this as the "genotype-phenotype map". T2 is the transformation due to natural selection, T3 are epigenetic relations that predict genotypes based on the selected phenotypes and finally T4 the rules of Mendelian genetics. Epigenetic inheritance is the transmission of information from a cell or multicellular organism to its descendants without that information being encoded in the nucleotide sequence of the gene. ... Developmental biology is the study of the process by which organisms grow and develop. ... The genotype-phenotype distinction refers to the fact that while genotype and phenotype of an organism are related, they do not necessarily coincide. ...


In practice, there are two bodies of evolutionary theory that exist in parallel, traditional population genetics operating in the genotype space and the biometric theory used in plant and animal breeding, operating in phenotype space. The missing part is the mapping between the genotype and phenotype space. This leads to a "sleight of hand" (as Lewontin terms it) whereby variables in the equations of one domain, are considered parameters or constants, where, in a full-treatment they would be transformed themselves by the evolutionary process and are in reality functions of the state variables in the other domain. The "sleight of hand" is assuming that we know this mapping. Proceeding as if we do understand it is enough to analyze many cases of interest. For example, if the phenotype is almost one-to-one with genotype (sickle-cell disease) or the time-scale is sufficiently short, the "constants" can be treated as such; however, there are many situations where it is inaccurate. This page is a candidate to be moved to Wiktionary. ... Plant breeding has been practiced for thousands of years. ... Selective breeding in domesticated animals is the process of developing a cultivated breed over time. ... Sickle-shaped red blood cells Sickle cell disease is a general term for a group of genetic disorders caused by sickle hemoglobin (Hgb S). ...


Population geneticists

The three founders of population genetics were the Britons Ronald Fisher, J.B.S. Haldane and the American Sewall Wright. Fisher and Wright had some fundamental disagreements and a controversy about the relative roles of selection and drift continued for much of the century between the Americans and the British. The Frenchman Gustave Mal├ęcot was also important early in the development of the discipline. John Maynard Smith was Haldane's pupil, whilst W.D. Hamilton was heavily influenced by the writings of Fisher. The American George R. Price worked with both Hamilton and Maynard Smith. On the American side, Richard Lewontin and the Japanese Motoo Kimura were heavily influenced by Wright. Luigi Luca Cavalli-Sforza is a Stanford-based population geneticist particularly interested in human population genetics. Sir Ronald Fisher Sir Ronald Aylmer Fisher, FRS (17 February 1890 – 29 July 1962) was a British eugenicist, evolutionary biologist, geneticist and statistician. ... John Burdon Sanderson Haldane (November 5, 1892 - December 1, 1964), who normally used J.B.S. as a first name, was a geneticist born in Scotland and educated at Eton and Oxford University. ... Sewall Green Wright (December 21, 1889– March 3, 1988) was an American geneticist known for his influential work on evolutionary theory. ... Gustave Malécot (December 28, 1911 — November 1998) was a French population geneticist. ... John Maynard Smith Professor John Maynard Smith, F.R.S. (6 January 1920 – 19 April 2004) was a British evolutionary biologist and geneticist. ... This article is about the British biologist Bill Hamilton. ... George R. Price (1922 - January 6, 1975) was a American population geneticist. ... Richard Lewontin Richard Charles Dick Lewontin (born March 29, 1929) is an American evolutionary biologist, geneticist and social commentator. ... Motoo Kimura (木村資生, born on November 13, 1924 in Okazaki, Aichi Prefecture - November 13, 1994) was a highly influential Japanese mathematical biologist, working in the field of theoretical population genetics. ... Categories: People stubs | 1922 births | Italian people | Population geneticists ... The Leland Stanford Junior University, commonly known as Stanford University (or simply Stanford), is a privately-funded American university in Stanford, California. ...


See also

Ecological genetics is the study of genetics (itself a field of biology) from an ecological perspective. ... In population genetics, Ewenss sampling formula, introduced by Warren Ewens, states that under certain conditions (specified below), if a random sample of n gametes is taken from a population and classified according to the gene at a particular locus then the probability that there are a1 alleles represented once... In evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between genotypes (or phenotypes) and replicatory success. ... The founder effect is an evolutionary phenomenon. ... Genetic diversity is a characteristic of ecosystems and gene pools that describes an attribute which is commonly held to be advantageous for survival -- that there are many different versions of otherwise similar organisms. ... The genotype-phenotype distinction refers to the fact that while genotype and phenotype of an organism are related, they do not necessarily coincide. ... Hardy–Weinberg principle for two alleles: the horizontal axis shows the two allele frequencies p and q, the vertical axis shows the genotype frequencies and the three possible genotypes are represented by the different glyphs The Hardy–Weinberg principle (HWP) (also Hardy–Weinberg equilibrium (HWE), or Hardy–Weinberg law) states... Microevolution is the occurrence of small-scale changes in gene frequencies in a population, over a few generations, also known as change at or below the species level. ... Molecular evolution is the process of the genetic material in populations of organisms changing over time. ... In evolutionary genetics, Mullers ratchet is the name given to the process by which the genomes of an asexual population accumulate deleterious mutations in an irreversible manner (hence the word ratchet), a process which the genomes of sexual populations can easily reverse thanks to recombination. ... Mutational meltdown refers to the process by which a small population accumulates deleterious mutations, which leads to loss of fitness and decline of the population size, which leads to further accumulation of deleterious mutations. ... A population bottleneck (or genetic bottleneck) is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing, and the population is reduced by 50% or more, often by several orders of magnitude. ... Quantitative genetics is the study of continuous traits (such as height or weight) and its underlying mechanisms. ... Selection is hierachically classified into natural and artificial selection. ... Species with a small population size are subject to a higher chance of extinction because their small population size makes them more vulnerable to genetic drift, resulting in stochastic variation in their gene pool, their demography and their environment. ...

References

  • J. Beatty. 1986. "The synthesis and the synthetic theory" in Integrating Scientific Disciplines, edited by W. Bechtel and Nijhoff. Dordrecht.
  • John Gillespie Population Genetics: A Concise Guide, Johns Hopkins Press, 1998 ISBN 0-8018-5755-4
  • Daniel Hartl Primer of Population Genetics, 3rd edition, Sinauer, 2000 ISBN 0878933042
  • Daniel Hartl and Andrew Clark Principles of Population Genetics, 3rd edition, Sinauer 1997 ISBN 0-87893-306-9
  • Richard C. Lewontin. 1974. The Genetic Basis of Evolutionary Change. Columbia University Press. New York.
  • James F. Crow and Motoo Kimura Introduction to Population Genetics Theory. 1972 Harper & Row

External links

  • History of population genetics
  • National Geographic: Atlas of the Human Journey (Haplogroup-based human migration maps)
Topics in population genetics
Key concepts: Hardy-Weinberg law | linkage disequilibrium | Fisher's fundamental theorem | neutral theory
Selection: natural | sexual | artificial | ecological
Genetic drift: small population size | population bottleneck | founder effect | coalescence
Founders: Ronald Fisher | J.B.S. Haldane | Sewall Wright
Related topics: evolution | microevolution | evolutionary game theory | fitness landscape
List of evolutionary biology topics
Subfields of genetics
Classical genetics | Ecological genetics | Molecular genetics | Population genetics | Quantitative genetics
Related topics: Genomics | Reverse genetics | Geneticist
Basic topics in evolutionary biology
Processes of evolution: evidence - macroevolution - microevolution - speciation
Mechanisms: selection - genetic drift - gene flow - mutation
Modes: anagenesis - catagenesis - cladogenesis
History: History of evolutionary thought - Charles Darwin - The Origin of Species - modern evolutionary synthesis
Subfields: population genetics - ecological genetics - human evolution - molecular evolution - phylogenetics - systematics - evo-devo
List of evolutionary biology topics | Timeline of evolution | Timeline of human evolution

  Results from FactBites:
 
Population genetics - Wikipedia, the free encyclopedia (710 words)
Population genetics is the study of the distribution of and change in allele frequencies under the influence of the four evolutionary forces: natural selection, genetic drift, mutation, and migration.
Population genetics was a vital ingredient in the modern evolutionary synthesis, its primary founders were Sewall Wright, J.
In practice, there are two bodies of evolutionary theory that exist in parallel, traditional population genetics operating in the genotype space and the biometric theory used in plant and animal breeding, operating in phenotype space.
Genetics - Wikipedia, the free encyclopedia (1560 words)
The word genetics was first suggested to describe the study of inheritance and the science of variation by the British scientist William Bateson in a personal letter to Adam Sedgwick, dated April 18, 1905.
The foundational discipline is population genetics which studies the distribution of and change in allele frequencies of genes under the influence of the four evolutionary forces: natural selection, genetic drift, mutation and migration.
The related subfield of quantitative genetics, which builds on population genetics, aims to predict the response to selection given data on the phenotype and relationships of individuals.
  More results at FactBites »

 
 

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