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Molecular evolution is the process of evolution at the scale of DNA, RNA, and proteins. Molecular evolution emerged as a scientific field in the 1960s as researchers from molecular biology, evolutionary biology and population genetics sought to understand recent discoveries on the structure and function of nucleic acids and protein. Some of the key topics that spurred development of the field have been the evolution of enzyme function, the use of nucleic acid divergence as a "molecular clock" to study species divergence, and the origin of non-functional or junk DNA. Recent advances in genomics, including whole-genome sequencing, high-throughput protein characterization, and bioinformatics have led to a dramatic increase in studies on the topic. In the 2000s, some of the active topics have been the role of gene duplication in the emergence of novel gene function, the extent of adaptive molecular evolution versus neutral drift, and the identification of molecular changes responsible for various human characteristics especially those pertaining to infection, disease, and cognition.

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Principles of molecular evolution

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Mutations

Mutations are permanent, transmissible changes to the genetic material (usually DNA or RNA) of a cell. Mutations can be caused by copying errors in the genetic material during cell division and by exposure to radiation, chemicals, or viruses, or can occur deliberately under cellular control during the processes such as meiosis or hypermutation. Mutations are considered the driving force of evolution, where less favorable (or deleterious) mutations are removed from the gene pool by natural selection, while more favorable (or beneficial) ones tend to accumulate. Neutral mutations do not affect the organism's chances of survival in its natural environment and can accumulate over time, which might result in what is known as punctuated equilibrium; the modern interpretation of classic evolutionary theory.

Causes of change in allele frequency

There are three known processes that affect the survival of a characteristic; or, more specifically, the frequency of an allele (variant of a gene):

  • Genetic drift describes changes in gene frequency that cannot be ascribed to selective pressures, but are due instead to events that are unrelated to inherited traits. This is especially important in small mating populations, which simply cannot have enough offspring to maintain the same gene distribution as the parental generation.
  • Gene flow or Migration: or gene admixture is the only one of the agents that makes populations closer genetically while building larger gene pools.
  • Selection, in particular natural selection produced by differential mortality and fertility. Differential mortality is the survival rate of individuals before their reproductive age. If they survive, they are then selected further by differential fertility – that is, their total genetic contribution to the next generation. In this way, the alleles that these surviving individuals contribute to the gene pool will increase the frequency of those alleles. Sexual selection, the attraction between mates that results from two genes, one for a feature and the other determining a preference for that feature, is also very important.

Molecular study of phylogeny

Molecular systematics is a product of the traditional field of systematics and molecular genetics. It is the process of using data on the molecular constitution of biological organisms' DNA, RNA, or both, in order to resolve questions in systematics, i.e. about their correct scientific classification or taxonomy from the point of view of evolutionary biology.

Molecular systematics has been made possible by the availability of techniques for DNA sequencing, which allow the determination of the exact sequence of nucleotides or bases in either DNA or RNA. At present it is still a long and expensive process to sequence the entire genome of an organism, and this has been done for only a few species. However, it is quite feasible to determine the sequence of a defined area of a particular chromosome. Typical molecular systematic analyses require the sequencing of around 1000 base pairs.

The driving forces of evolution

Depending on the relative importance assigned to the various forces of evolution, three perspectives provide evolutionary explanations for molecular evolution.[1]

While recognizing the importance of random drift for silent mutations,[2] selectionists hypotheses argue that balancing and positive selection are the driving forces of molecular evolution. Those hypotheses are often based on the broader view called panselectionism, the idea that selection is the only force strong enough to explain evolution, relaying random drift and mutations to minor roles.[1]

Neutralists hypotheses emphasize the importance of mutation, purifying selection and random genetic drift.[3] The introduction of the neutral theory by Kimura,[4] quickly followed by King and Jukes' own findings,[5] lead to a fierce debate about the relevance of neodarwinism at the molecular level. The Neutral theory of molecular evolution states that most mutations are deleterious and quickly removed by natural selection, but of the remaining ones, the vast majority are neutral with respect to fitness while the amount of advantageous mutations is vanishingly small. The fate of neutral mutations are governed by genetic drift, and contribute to both nucleotide polymorphism and fixed differences between species. [6][7][8]

Mutationists hypotheses emphasize random drift and biases in mutation patterns.[9] Sueoka was the first to propose a modern mutationist view. He proposed that the variation in GC content was not the result of positive selection, but a consequence of the GC mutational pressure.[10]

Related fields

An important area within the study of molecular evolution is the use of molecular data to determine the correct biological classification of organisms. This is called molecular systematics or molecular phylogenetics.

Tools and concepts developed in the study of molecular evolution are now commonly used for comparative genomics and molecular genetics, while the influx of new data from these fields has been spurring advancement in molecular evolution.

Key researchers in molecular evolution

Some researchers who have made key contributions to the development of the field:

Journals and societies

Journals dedicated to molecular evolution include Molecular Biology and Evolution, Journal of Molecular Evolution, and Molecular Phylogenetics and Evolution. Research in molecular evolution is also published in journals of genetics, molecular biology, genomics, systematics, or evolutionary biology. The Society for Molecular Biology and Evolution publishes the journal "Molecular Biology and Evolution" and holds an annual international meeting.

See also

Further reading

  • Li, W.-H. (2006). Molecular Evolution. Sinauer. ISBN 0878934804.  
  • Lynch, M. (2007). The Origins of Genome Architecture. Sinauer. ISBN 0878934847.  

References

  1. ^ a b Graur, D. and Li, W.-H. (2000). Fundamentals of molecular evolution. Sinauer.  
  2. ^ Gillespie, J. H (1991). The Causes of Molecular Evolution. Oxford University Press, New York. ISBN 0-19-506883-1.  
  3. ^ Kimura, M. (1983). The Neutral Theory of Molecular Evolution. Cambridge University Press, Cambridge. ISBN 0-521-23109-4.  
  4. ^ Kimura, Motoo (1968). "Evolutionary rate at the molecular level". Nature 217: 624–626. doi:10.1038/217624a0. http://www2.hawaii.edu/~khayes/Journal_Club/fall2006/Kimura_1968_Nature.pdf.  
  5. ^ King, J.L. and Jukes, T.H. (1969). "Non-Darwinian Evolution". Science 164: 788–798. doi:10.1126/science.164.3881.788. PMID 5767777. http://www.blackwellpublishing.com/ridley/classictexts/king.pdf.  
  6. ^ Nachman M. (2006). "Detecting selection at the molecular level" in: Evolutionary Genetics: concepts and case studies. pp. 103–118.  
  7. ^ The nearly neutral theory expanded the neutralist perspective, suggesting that several mutations are nearly neutral, which means both random drift and natural selection is relevant to their dynamics.
  8. ^ Ohta, T (1992). "The nearly neutral theory of molecular evolution". Annual Review of Ecology and Systematics 23: 263–286. doi:10.1146/annurev.es.23.110192.001403.  
  9. ^ Nei, M. (2005). "Selectionism and Neutralism in Molecular Evolution". Molecular Biology and Evolution 22(12): 2318–2342. doi:10.1093/molbev/msi242. PMID 16120807.  
  10. ^ Sueoka, N. (1964). "On the evolution of informational macromolecules". in In: Bryson, V. and Vogel, H.J.. Evolving genes and proteins. Academic Press, New-York. pp. 479–496.  

Study guide

Up to date as of January 14, 2010

From Wikiversity

Welcome to the Wikiversity Molecular Evolution Project.

Contents

Content summary

Participants in this project explore the molecular evolution of DNA, RNA and proteins.

Learning materials

Learning materials and learning projects are located in the main Wikiversity namespace. Simply make a link to the name of the lesson (lessons are independent pages in the main namespace) and start writing!

You should also read about the Wikiversity:Learning model. Lessons should center on learning activities for Wikiversity participants. Learning materials and learning projects can be used by multiple projects. Cooperate with other departments that use the same learning resource.

Texts

Activities

  • Select a protein of interest and explore which living organisms have a gene for that type of protein.
  • etc.

Readings

Each activity has a suggested associated background reading selection.

References

Additional helpful readings include:

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Active participants in this Learning Group

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  • AFriedman

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Simple English

Molecular evolution is the process of evolution in DNA, RNA, and proteins.

Molecular evolution emerged as a scientific field in the 1960s as researchers from molecular biology, evolutionary biology and population genetics sought to understand the structure and function of nucleic acids and protein. Some of the key topics have been the evolution of enzyme function, the use of nucleic acid changes as a molecular clock to study species divergence, and the origin of non-functional or junk DNA.

Recent advances in genomics, including whole-genome sequencing, and bioinformatics have led to a dramatic increase in studies on the topic. In the 2000s, the role of gene duplication, the extent of adaptive molecular evolution versus neutral genetic drift, and the identification of molecular changes responsible for various human characteristics especially those pertaining to infection, disease, and cognition.

Molecular study of phylogeny

Molecular systematics is the process of using data on the DNA, RNA, or proteins to resolve questions in phylogeny and taxonomy.[1][2] The idea is to place groups in their correct postion on the evolutionary tree. This corrects their biological classification from the point of view of evolution. The technique has already led to major changes in the taxonomy of living things, including the names for higher categories, which had been stable for well over a century.

Molecular systematics has been made possible by the techniques for sequencing, which allow the determination of the exact sequence of nucleotides or bases in either DNA or RNA. At present it is still a long and expensive process to sequence the entire genome of an organism, and this has been done for only a few species. However, it is quite feasible to determine the sequence of a defined area of a particular chromosome. Typical molecular systematic analyses require the sequencing of around 1000 base pairs.

References

  1. Graur D. and Li W.-H. (2000). Fundamentals of molecular evolution. Sinauer. 
  2. Gillespie, J.H. (1991). The causes of molecular evolution. Oxford University Press, New York. ISBN 0-19-506883-1. 


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