Navigation Links
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 is the theory that 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.

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 core of the modern synthesis.

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:

(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.

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, and it is certainly true that it is sufficient to proceed as if we do understand it, to analyze many cases of interest. For example, if the phenotype is almost one-to-one with genotype (sickle-cell anemia) or the time-scale is sufficiently short, the "constants" can be treated as such; however, there are many situations where it is inaccurate.

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 Malcot 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 Stanford-based population geneticist particularly interested in human population genetics.

See also

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.

External links




'"/>


(Date:9/16/2014)... Philadelphia, PA, September 16, 2014 Schizophrenia is associated ... A growing body of research suggests that the relationship ... effort by patients to use nicotine to self-medicate symptoms ... new study, published in the current issue of ... authors found that the level of nicotine receptors in ...
(Date:9/16/2014)... responsible for practically all vital functions in an ... signals, transport particular substances and control immune system ... do not function independently of each other, but ... the protein networks, you find many similarities with ... TUM,s Chair of Plant Systems Biology. "Some proteins ...
(Date:9/15/2014)... processes from digestion to disease resistance. Despite the fact ... on the planet, more is known about belly-button bacteria ... and colleagues working on Panama,s Barro Colorado Island discovered ... home to more than 400 different kinds of bacteria. ... than 7,000 different kinds. , Bacteria in tropical forests ...
Breaking Biology News(10 mins):Smoking and schizophrenia linked by alterations in brain nicotine signals 2Good networkers make prime targets 2Smithsonian scientists discover tropical tree microbiome in Panama 2
... St. Louis, MO, June 1, 2010 Making food choices ... according to a new study comparing the nutritional content of ... the June issue of the Journal of the American ... diet consisting entirely of advertised foods would contain 25 times ...
... Arbor, Mich. University of Michigan scientists have provided the ... brain that influences the effectiveness of serotonin-related antidepressants, such as ... ahead of print in the journal Proceedings of the ... a more targeted treatment of depression and anxiety with fewer ...
... have identified three new susceptibility genes in a genome-wide ... by the Genome Institute of Singapore (GIS), a biomedical ... Research (A*STAR), and the Sun Yat-Sen University Cancer Centre, ... understanding of the important role played by host genetic ...
Cached Biology News:TV food advertisements promote imbalanced diets 2Animal study reveals new target for antidepressants 2Scientists find genes associated with throat cancer through study of over 10,000 subjects 2Scientists find genes associated with throat cancer through study of over 10,000 subjects 3
Other biology definitionOther Tags