History of genetics
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/* The genomics era */ Rmv wikilink...it is already earlier in paragraph
[[Image:Mendel.png|frame|right|[[Gregor Mendel]], the "father of genetics"]]
The '''history of [[genetics]]''' is generally held to have started with the work of an [[Augustinian]] [[monk]], [[Gregor Mendel]]. [[Experiments on Plant Hybridization|His work]] on pea plants, published in 1866, described what came to be known as [[Mendelian inheritance]]. In the centuries before—and for several decades after—Mendel's work, a wide variety of theories of [[heredity]] proliferated (see below). 1900 marked the "rediscovery of Mendel" by [[Hugo de Vries]], [[Carl Correns]] and [[Erich von Tschermak]], and by 1915 the basic principles of Mendelian genetics had been applied to a wide variety of organisms—most notably the fruit fly ''[[Drosophila melanogaster]]''. Led by [[Thomas Hunt Morgan]] and his fellow "drosophilists", geneticists developed the [[Mendelian-chromosome theory of heredity]], which was widely accepted by 1925. Alongside experimental work, mathematicians developed the statistical framework of [[population genetics]], bring genetical explanations into the study of [[evolution]].
With the basic patterns of genetic inheritance established, many biologists turned to investigations of the physical nature of the [[gene]]. In the 1940s and early 1950s, experiments pointed to [[DNA]] as the portion of chromosomes (and perhaps other nucleoproteins) that held genes. A focus on new model organisms such as viruses and bacteria, along with the discovery of the double helical structure of DNA in 1953, marked the transition to the era of [[molecular genetics]]. In the following years, chemists developed techniques for sequencing both nucleic acids and proteins, while others worked out the relationship between the two forms of biological molecules: the [[genetic code]]. The regulation of [[gene expression]] became a central issue in the 1960s; by the 1970s gene expression could be controlled and manipulated through [[genetic engineering]]. In the last decades of the 20th century, many biologists focused on large-scale genetics projects, sequencing entire genomes.
== Pre-Mendelian ideas on heredity ==
{{see also|Heredity}}
===Ancient theories===
The most influential early theories of heredity were that of [[Hippocrates]] and [[Aristotle]]. Hippocrates' theory (possibly based on the teachings of [[Anaxagoras]]) was similar to Darwin's later ideas on [[pangenesis]], involving heredity material that collects from throughout the body. Aristotle suggested instead that the (nonphysical) [[Eidos|form-giving principle]] of an organism was transmitted through semen (which he considered to be a purified form of blood) and the mother's menstrual blood, which interacted in the womb to direct an organism's early development. For both Hippocrates and Aristotle—and nearly all Western scholars through to the late 19th century—the [[inheritance of acquired characters]] was a supposedly well-established fact that any adequate theory of heredity had to explain. At the same time, individual species were taken to have a [[essentialism|fixed essence]]; such inherited changes were merely superficial.<ref>Mayr, ''The Growth of Biological Thought'', pp 635-640</ref>
===Plant systematics and hybridization===
{{see also|History of plant systematics}}
In the 18th century, with increased knowledge of plant and animal diversity and the accompanying increased focus on [[taxonomy]], new ideas about heredity began to appear. [[Linnaeus]] and others (among them [[Joseph Gottlieb Kölreuter]], [[Carl Friedrich von Gärtner]], and [[Charles Naudin]]) conducted extensive experiments with hybridization, especially species [[Hybrid (biology)|hybrids]]. Species hybridizers described a wide variety of inheritance phenomena, include hybrid sterility and the high variability of [[back-crossing|back-crosses]].<ref>Mayr, ''The Growth of Biological Thought'', pp 640-649</ref>
Plant breeders were also developing an array of stable [[Variety (botany)|varieties]] in many important plant species. In the early 19th century, [[Augustin Sageret]] established the concept of [[Dominance relationship|dominance]], recognizing that when some plant varieties are crossed, certain characters (present in one parent) usually appear in the offspring; he also found that some ancestral characters found in neither parent may appear in offspring. However, plant breeders made little attempt to establish a theoretical foundation for their work or to share their knowledge with current work of physiology.<ref>Mayr, ''The Growth of Biological Thought'', pp 649-651</ref>
== Mendel ==
In breeding experiments between 1856 and 1865, [[Gregor Mendel]] first traced inheritance patterns of certain traits in pea plants and showed that they obeyed simple statistical rules. Although not all features show these patterns of [[Mendelian inheritance]], his work acted as a proof that application of statistics to inheritance could be highly useful. Since that time many more complex forms of inheritance have been demonstrated.
From his statistical analysis Mendel defined a concept that he described as an ''[[allele]]'', which was the fundamental unit of heredity. The term ''allele'' as Mendel used it{{Fact|date=February 2007}} is nearly synonymous with the term ''gene'', and now means a specific variant of a particular gene.
Mendel's work was published in 1866 as ''"Versuche über Pflanzen-Hybriden" ([[Experiments on Plant Hybridization]])'' in the ''Verhandlungen des Naturforschenden Vereins zu Brünn (Proceedings of the Natural History Society of Brünn)'', following two lectures he gave on the work in early 1865.
== Post-Mendel, pre-re-discovery==
Mendel's work was published in a relatively obscure [[scientific journal]], and it was not given any attention in the scientific community. Instead, discussions about modes of heredity were galvanized by [[Charles Darwin|Darwin]]'s theory of [[evolution]] by natural selection, in which mechanisms of non-[[Lamarckian]] heredity seemed to be required. Darwin's own theory of heredity, [[pangenesis]], did not meet with any large degree of acceptance. A more mathematical version of pangenesis, one which dropped much of Darwin's Lamarckian holdovers, was developed as the "biometrical" school of heredity by Darwin's cousin, [[Francis Galton]]. Under Galton and his successor [[Karl Pearson]], the biometrical school attempted to build statistical models for heredity and evolution, with some limited but real success, though the exact methods of heredity were unknown and largely unquestioned.
== Classical genetics ==
The significance of Mendel's work was not understood until early in the twentieth century, after his death, when his research was re-discovered by other scientists working on similar problems. [[Hugo de Vries]], [[Carl Correns]] and [[Erich von Tschermak]]
There was then a feud between [[William Bateson|Bateson]] and [[Karl Pearson|Pearson]] over the hereditary mechanism. [[Ronald Fisher|Fisher]] solved this in [[The Correlation Between Relatives on the Supposition of Mendelian Inheritance]]
:[[1865]] [[Gregor Mendel]]'s paper, ''[[Experiments on Plant Hybridization]]''
:[[1869]] [[Friedrich Miescher]] discovers a weak acid in the nuclei of [[Leukocyte|white blood cells]] that today we call [[DNA]]
:[[1880]]-[[1890]] [[Walther Flemming]], [[Eduard Strasburger]], and [[Edouard van Beneden]] elucidate chromosome distribution during [[cell division]]
:[[1889]] [[Hugo de Vries]] postulates that "inheritance of specific traits in organisms comes in particles", naming such particles "(pan)genes"<ref name="pangen">Vries, H. de (1889) ''Intracellular Pangenesis'' [http://www.esp.org/books/devries/pangenesis/facsimile/] ("pan-gene" definition on page 7 and 40 of this 1910 translation in English)</ref>
:[[1903]] [[Walter Sutton]] hypothesizes that chromosomes, which segregate in a Mendelian fashion, are hereditary units<ref name="100 Years Ago: Walter Sutton and the Chromosome Theory of Heredity">{{cite journal | author=Ernest W. Crow and James F. Crow| title=100 Years Ago: Walter Sutton and the Chromosome Theory of Heredity| journal=Genetics| year=2002| volume=160| url=http://www.genetics.org/cgi/content/full/160/1/1| pages=1–4| pmid=11805039}}</ref>
:[[1905]] [[William Bateson]] coins the term "genetics" in a letter to [[Adam Sedgwick]]<ref>[http://www.jic.ac.uk/corporate/about/bateson.htm Online copy of William Bateson's letter to Adam Sedgwick]</ref> and at a meeting in 1906<ref name="bateson_genetics">{{cite conference | author=Bateson, William | title=The Progress of Genetic Research |editor=Wilks, W. (editor) | booktitle=Report of the Third 1906 International Conference on Genetics: Hybridization (the cross-breeding of genera or species), the cross-breeding of varieties, and general plant breeding|publisher=Royal Horticultural Society | location=London | year=1907}}
:Although the conference was titled "International Conference on Hybridisation and Plant Breeding", Wilks changed the title for publication as a result of Bateson's speech.</ref>
:[[1908]] [[Hardy-Weinberg law]] derived.
:[[1910]] [[Thomas Hunt Morgan]] shows that genes reside on chromosomes
:[[1913]] [[Alfred Sturtevant]] makes the first [[genetic map]] of a chromosome
:[[1913]] [[Gene map]]s show chromosomes containing linear arranged genes
:[[1918]] [[Ronald Fisher]] publishes "[[The Correlation Between Relatives on the Supposition of Mendelian Inheritance]]" the [[modern synthesis]] of genetics and [[evolutionary biology]] starts. See [[population genetics]].
:[[1928]] [[Frederick Griffith]] discovers that hereditary material from dead [[bacteria]] can be incorporated into live bacteria (see [[Griffiths experiment]])
:[[1931]] [[Chromosomal crossover|Crossing over]] is identified as the cause of [[recombination]]
:[[1933]] [[Jean Brachet]] is able to show that [[DNA]] is found in [[chromosomes]] and that [[RNA]] is present in the [[cytoplasm]] of all cells.
:[[1941]] [[Edward Lawrie Tatum]] and [[George Wells Beadle]] show that genes code for [[protein]]s; see the original [[central dogma of genetics]]
== The DNA era ==
[[Image:JamesDWatson.jpg|thumb|James Watson and colleagues discovered the structure of DNA]]
:[[1944]] [[Oswald Theodore Avery]], [[Colin McLeod]] and [[Maclyn McCarty]] isolate [[DNA]] as the genetic material (at that time called [[transforming principle]])<ref name="dna_transforming">{{cite journal | author=Avery, MacLeod, and McCarty| title=Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III| journal=Journal of Experimental Medicine| year=1944| volume=79| issue=1| pages=137–58| doi=10.1084/jem.79.2.137}}[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=33226 35th anniversary reprint available]</ref>
:[[1950]] [[Erwin Chargaff]] shows that the four nucleotides are not present in nucleic acids in stable proportions, but that some general rules appear to hold (e.g., that the amount of [[adenine]], A, tends to be equal to that of [[thymine]], T). [[Barbara McClintock]] discovers [[transposon]]s in [[maize]]
:[[1952]] The [[Hershey-Chase experiment]] proves the genetic information of [[phage]]s (and all other organisms) to be DNA
:[[1953]] DNA structure is resolved to be a double [[helix]] by [[James D. Watson]] and [[Francis Crick]]<ref>Watson JD, Crick FH, Molecular structure of nucleic acids; a structure for deoxyribose nucleic acid, Nature. 1953 Apr 25;171(4356):737-8</ref>
:[[1956]] [[Joe Hin Tjio]] and [[Albert Levan]] established the correct [[chromosome]] number in humans to be 46
:[[1958]] The [[Meselson-Stahl experiment]] demonstrates that DNA is [[semiconservative replication|semiconservatively replicated]]
:[[1961]]-[[1967]] Combined efforts of scientists "crack" the [[genetic code]], including [[Marshall Nirenberg]], [[Har Gobind Khorana]], [[Sydney Brenner]] & [[Francis Crick]]
:[[1964]] [[Howard Temin]] showed using [[RNA virus]]es that the direction of DNA to RNA transcription can be reversed
:[[1970]] [[Restriction enzyme]]s were discovered in studies of a bacterium, ''[[Haemophilus influenzae]]'', enabling scientists to cut and paste DNA
== The genomics era ==
See [[genomics]], [[history of genomics]]
:[[1972]], [[Walter Fiers]] and his team at the Laboratory of Molecular Biology of the [[University of Ghent]] ([[Ghent]], [[Belgium]]) were the first to determine the sequence of a gene: the gene for [[bacteriophage MS2]] coat protein.<ref>Min Jou W, Haegeman G, Ysebaert M, Fiers W., Nucleotide sequence of the gene coding for the bacteriophage MS2 coat protein, Nature. 1972 May 12;237(5350):82-8</ref>
:[[1976]], [[Walter Fiers]] and his team determine the complete nucleotide-sequence of bacteriophage MS2-RNA<ref>Fiers W et al., Complete nucleotide-sequence of bacteriophage MS2-RNA - primary and secondary structure of replicase gene, Nature, 260, 500-507, 1976</ref>
:[[1977]] DNA is [[sequencing|sequenced]] for the first time by [[Fred Sanger]], [[Walter Gilbert]], and [[Allan Maxam]] working independently. Sanger's lab sequence the entire [[genome]] of [[Phi X 174|bacteriophage Φ-X174]].<ref>Sanger F, Air GM, Barrell BG, Brown NL, Coulson AR, Fiddes CA, Hutchison CA, Slocombe PM, Smith M., Nucleotide sequence of bacteriophage phi X174 DNA, Nature. 1977 Feb 24;265(5596):687-95</ref>
:[[1983]] [[Kary Banks Mullis]] discovers the [[polymerase chain reaction]] enabling the easy amplification of DNA
:[[1989]] The [[human]] gene that encodes the [[Cystic fibrosis transmembrane conductance regulator|CFTR]] protein was sequenced by [[Francis Collins (geneticist)|Francis Collins]] and [[Lap-Chee Tsui]]. Defects in this gene cause [[cystic fibrosis]].
:[[1995]] The genome of ''Haemophilus influenzae'' is the first genome of a free living organism to be sequenced
:[[1996]] ''[[Saccharomyces cerevisiae]]'' is the first [[eukaryote]] genome sequence to be released
:[[1998]] The first genome sequence for a multicellular eukaryote, ''[[Caenorhabditis elegans]]'', is released
:[[2001]] First draft sequences of the human genome are released simultaneously by the [[Human Genome Project]] and [[Celera Genomics]].
:[[2003]] ([[14 April]]) Successful completion of Human Genome Project with 99% of the genome sequenced to a 99.99% [[accuracy]] [http://www.genoscope.cns.fr/externe/English/Actualites/Presse/HGP/HGP_press_release-140403.pdf]
==See also==
*[[List of sequenced eukaryotic genomes]]
==External links==
* [http://www.mendelweb.org/MWolby.html Olby's "Mendel, Mendelism, and Genetics," at MendelWeb]
* http://www.accessexcellence.org/AE/AEPC/WWC/1994/geneticstln.html
* http://www.esp.org/books/sturt/history/
* http://cogweb.ucla.edu/ep/DNA_history.html
* http://news.bbc.co.uk/1/hi/in_depth/sci_tech/2000/human_genome/749026.stm
==Further reading==
* [[Elof Axel Carlson]], ''Mendel's Legacy: The Origin of Classical Genetics'' (Cold Spring Harbor Laboratory Press, 2004.) ISBN 0-87969-675-3
==References==
<references/>
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