Molecular phylogeny is the use of the structure of molecules to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a so-called phylogenetic tree. A phylogenetic tree is a tree showing the evolutionary interrelationships among various species or other entities that are believed to have a common ancestor. ...

Every living organism contains DNA, RNA, and proteins. Closely related organisms generally have a high degree of agreement in the molecular structure of these substances, while the molecules of organisms distantly related usually show a pattern of dissimilarity. Molecular phylogeny uses such data to build a "relationship tree" that shows the probable evolution of various organisms. Not until recent decades, however, has it been possible to isolate and identify these molecular structures. In biology and ecology, an organism (in Greek organon = instrument) is a complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid —usually in the form of a double helix— that contains the genetic instructions specifying the biological development of all cellular forms of life, and most viruses. ... Ribonucleic acid (RNA) is a nucleic acid polymer consisting of covalently bound nucleotides. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Geometry of the water molecule Molecules have fixed equilibrium geometries--bond lengths and angles--that are dictated by the laws of quantum mechanics. ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... A speculative phylogenetic tree of all living things, based on rRNA gene data, showing the separation of the three domains, bacteria, archaea, and eukaryotes. ...

Another application of the techniques that make this is possible can be seen in the very limited field of human genetics, such as the ever more popular use of genetic testing to determine a child's paternity, as well as the emergence of a new branch of criminal forensics focused on genetic evidence. Genetic testing allows the genetic diagnosis of vulnerabilities to inherited diseases, and can also be used to determine a persons ancestry. ... Paternity is the social and legal acknowledgment of the parental relationship between a father and his child. ... Forensic science (often shortened to forensics) is the application of a broad spectrum of sciences to answer questions of interest to the legal system. ...

The effect on traditional scientific classification schemes in the biological sciences has been dramatic as well. Work that was once immensely labor- and materials-intensive can now be done quickly and easily, leading to yet another source of information becoming available for systematic and taxonomic appraisal. This partical kind of data has become so popular that taxonomical schemes based solely on molecular data may be encountered. Proponents even claim that taxonomy was previously based on morphology alone, which of course is utter fable. Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... Comparative anatomy is the study of similarities and differences in organisms. ...

Further reading

• Page, R. D. M. & Holmes, E. C. 1998. Molecular evolution: a phylogenetic approach. Blackwell Science, Oxford. ISBN 0865428891 (A small book).
• Hillis, D. M. & Moritz, C. 1996. Molecular systematics. 2nd ed. Sinauer Associates Incorporated. ISBN 0878932828. (A big book.)
• Felsenstein, J. 2004. Inferring phylogenies. Sinauer Associates Incorporated. ISBN 0878931775 (A big book not yet read.)

Joseph Joe Felsenstein is Professor of Genome Sciences and Biology and Adjunct Professor of Computer Science and Statistics at the Department of Genome Sciences of the University of Washington in Seattle. ...

See also

• DNA barcode
• molecular clock
• molecular evolution
• phylogenetics