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Encyclopedia > Molecular clock

The molecular clock (based on the molecular clock hypothesis (MCH)) is a technique in genetics, which researchers use to date when two species diverged. It deduces elapsed time from the number of minor differences between their DNA sequences. Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ... In biology, a species is a kind of organism. ... Speciation refers to the appearance of a new species of life on earth, particularly as seen in the fossil record. ... A DNA sequence (sometimes genetic sequence) is a succession of letters representing the primary structure of a real or hypothetical DNA molecule or strand, The possible letters are A, C, G, and T, representing the four nucleotide subunits of a DNA strand (adenine, cytosine, guanine, thymine), and typically these are...

The notion of a "molecular clock" was first attributed to Emile Zuckerkandl and Linus Pauling who, in 1962, noticed that the quantity of amino acid differences in hemoglobin between lineages roughly matched the known evolutionary rate of divergence based upon fossil evidence. They generalized this observation to assert that the rate of evolutionary change of any specified protein was approximately constant over time and over different lineages. It has been applied to DNA sequence evolution also, particularly neutral evolution. Pauling lectured at Osaka University in 1955. ... 1962 was a common year starting on Monday (link will take you to calendar). ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... 3-dimensional structure of hemoglobin Hemoglobin or haemoglobin is the iron-containing oxygen-transport metalloprotein in the red cells of the blood in mammals and other animals. ... Charles Darwin, the father of modern evolutionary theory In the life sciences, evolution is a change in the traits of living organisms over generations, including the emergence of new species. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Space-filling model of a section of DNA molecule Deoxyribose nucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and many viruses). ... A protein primary structure is a chain of amino acids. ... The neutral theory of molecular evolution (also, simply the neutral theory of evolution) is an influential theory that was introduced with provocative effect by Motoo Kimura in the late 1960s and early 1970s. ...

Later Allan Wilson and Vince Sarich built upon this work and the work of Motoo Kimura (1968) observed and formalized that rare spontaneous errors in DNA replication cause the mutations that drive molecular evolution, and that the accumulation of evolutionarily "neutral" differences between two sequences could be used to measure time, if the error rate of DNA replication could be calibrated. One method of calibrating the error rate was to use as references pairs of groups of living species whose date of speciation was already known from the fossil record. Allan Wilson. ... Motoo Kimura (November 13, 1924 - November 13, 1994) was a highly influential Japanese mathematical biologist, working in the field of theoretical population genetics. ... DNA replication. ... This article is about mutation in biology, for other meanings see: mutation (disambiguation). ... Molecular evolution is the process of the genetic material in populations of organisms changing over time. ...

Originally, it was assumed that the DNA replication error rate was constant--not just over time, but across all species and every part of a genome that you might want to compare. Because the enzymes that replicate DNA differ only very slightly between species, the assumption seemed reasonable a priori. As molecular evidence has accumulated, the constant-rate assumption has proven false--or at least overly general. However while the MCH canot be blindly assumed to be true, it does hold in many cases, and these can be tested for. For example, molecular clock users are developing workaround solutions using a number of statistical approaches including maximum likelihood techniques and later Bayesian modeling. In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... In statistics, the method of maximum likelihood, pioneered by geneticist and statistician Sir Ronald A. Fisher, is a method of point estimation, that uses as an estimate of an unobservable population parameter the member of the parameter space that maximizes the likelihood function. ... Bayesian inference is statistical inference in which probabilities are interpreted not as frequencies or proportions or the like, but rather as degrees of belief. ...

The molecular clock technique is an important tool in molecular systematics, the use of molecular genetics information to determine the correct scientific classification of organisms. Knowledge of approximately-constant rate of molecular evolution in particular sets of lineages also facilitates establishing the dates of phylogenetic events. Molecular systematics is a product of the traditional field of systematics and the growing field of bioinformatics. ... Molecular genetics is the field of biology which studies the structure and function of genes at a molecular level. ... Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... A phylogeny (or phylogenesis) is the origin and evolution of a set of organisms, usually of a species. ...

See also

The neutral theory of molecular evolution (also, simply the neutral theory of evolution) is an influential theory that was introduced with provocative effect by Motoo Kimura in the late 1960s and early 1970s. ... An artists impression of Mitochondrial Eve who probably lived in Africa, about 150,000 years ago. ... In human genetics, Y-chromosomal Adam is the male counterpart to mitochondrial Eve: a real or hypothetical single male human ancestor from whom all male Y chromosomes are descended. ...


  • ZUCKERKANDL, E., and L. PAULING, 1962 "Molecular disease, evolution, and genetic heterogeneity", pp. 189–225 in Horizons in Biochemistry, edited by M. KASHA and B. PULLMAN. Academic Press, New York.
  • ZUCKERKANDL, E., and L. PAULING, 1965 "Evolutionary divergence and convergence in proteins", pp. 97–166 in Evolving Genes and Proteins, edited by V. BRYSON and H. J. VOGEL. Academic Press, New York.
  • Vincent M. Sarich and Allan C. Wilson. "Immunological time scale for hominid evolution". Science 158, 1967, pp. 1200-1203.
  • Kimura, Motoo (1968). "Evolutionary Rate at the Molecular Level", Nature Vol. 217, pp. 624-626.

Science is the journal of the American Association for the Advancement of Science. ... 1967 was a common year starting on Sunday (the link is to a full 1967 calendar). ...

External links

  • The Neutral Theory of Molecular Evolution (http://home.wxs.nl/~gkorthof/kortho37.htm)
  • The Molecular Clock Problem (http://www.cs.unc.edu/~plaisted/ce/clock.html)
  • Allan Wilson and the molecular clock (http://awcmee.massey.ac.nz/aw.htm)

  Results from FactBites:
Encyclopedia of Molecular Biology, Volumes 1-4 (97 words)
The field of molecular biology has revolutionized the study of biology.
The applications to medicine are enormous, ranging from diagnostic techniques for disease and genetic disorders, to drugs, to gene therapy.
Focusing on the fundamentals of molecular biology and encompassing all aspects of the expression of genetic information, this encyclopedia will become the first point of reference for both newcomers and established professionals in molecular biology needing to learn about any particular aspect of the field.
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