- History of genetics
The history of
geneticsis generally held to have started with the work of an Augustinian monk, Gregor Mendel. 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 heredityproliferated (see below). 1900 marked the "rediscovery of Mendel" by Hugo de Vries, Carl Corrensand 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 Morganand 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 DNAas 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 expressionbecame 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
The most influential early theories of heredity were that of
Hippocratesand 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) 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 characterswas 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 fixed essence; such inherited changes were merely superficial. [Mayr, "The Growth of Biological Thought", pp 635-640]
Plant systematics and hybridization
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. Linnaeusand others (among them Joseph Gottlieb Kölreuter, Carl Friedrich von Gärtner, and Charles Naudin) conducted extensive experiments with hybridization, especially species hybrids. Species hybridizers described a wide variety of inheritance phenomena, include hybrid sterility and the high variability of back-crosses. [Mayr, "The Growth of Biological Thought", pp 640-649]
Plant breeders were also developing an array of stable varieties in many important plant species. In the early 19th century,
Augustin Sageretestablished the concept of 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. [Mayr, "The Growth of Biological Thought", pp 649-651]
In breeding experiments between 1856 and 1865,
Gregor Mendelfirst 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 itFact|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.
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 Darwin's theory of evolutionby natural selection, in which mechanisms of non- Lamarckianheredity 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.
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 Corrensand Erich von Tschermak
Gregor Mendel's paper, " Experiments on Plant Hybridization":1869 Friedrich Miescherdiscovers a weak acid in the nuclei of white blood cells that today we call DNA:1880-1890 Walther Flemming, Eduard Strasburger, and Edouard van Benedenelucidate chromosome distribution during cell division:1889 Hugo de Vriespostulates that "inheritance of specific traits in organisms comes in particles", naming such particles "(pan)genes"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)] :1903 Walter Suttonhypothesizes that chromosomes, which segregate in a Mendelian fashion, are hereditary unitscite 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] :1905 William Batesoncoins the term "genetics" in a letter to Adam Sedgwick[ [http://www.jic.ac.uk/corporate/about/bateson.htm Online copy of William Bateson's letter to Adam Sedgwick] ] and at a meeting in 1906cite 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.] :1908 Hardy-Weinberg lawderived.:1910 Thomas Hunt Morganshows that genes reside on chromosomes:1913 Alfred Sturtevantmakes the first genetic mapof a chromosome:1913 Gene maps show chromosomes containing linear arranged genes:1918 Ronald Fisherpublishes " The Correlation Between Relatives on the Supposition of Mendelian Inheritance" the modern synthesisof genetics and evolutionary biologystarts. See population genetics.:1928 Frederick Griffithdiscovers that hereditary material from dead bacteriacan be incorporated into live bacteria (see Griffiths experiment):1931 Crossing over is identified as the cause of recombination:1933 Jean Brachetis able to show that DNAis found in chromosomesand that RNAis present in the cytoplasmof all cells.:1941 Edward Lawrie Tatumand George Wells Beadleshow that genes code for proteins; see the original central dogma of genetics
The DNA era
Oswald Theodore Avery, Colin McLeodand Maclyn McCartyisolate DNAas the genetic material (at that time called transforming principle)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] ] :1950 Erwin Chargaffshows 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 McClintockdiscovers transposons in maize:1952 The Hershey-Chase experimentproves the genetic information of phages (and all other organisms) to be DNA:1953 DNA structure is resolved to be a double helixby James D. Watsonand Francis Crick[Watson JD, Crick FH, Molecular structure of nucleic acids; a structure for deoxyribose nucleic acid, Nature. 1953 Apr 25;171(4356):737-8] :1956 Joe Hin Tjioand Albert Levanestablished the correct chromosomenumber in humans to be 46:1958 The Meselson-Stahl experimentdemonstrates that DNA is semiconservatively replicated:1961-1967 Combined efforts of scientists "crack" the genetic code, including Marshall Nirenberg, Har Gobind Khorana, Sydney Brenner& Francis Crick:1964 Howard Teminshowed using RNA viruses that the direction of DNA to RNA transcription can be reversed:1970 Restriction enzymes were discovered in studies of a bacterium, " Haemophilus influenzae", enabling scientists to cut and paste DNA
The genomics era
genomics, history of genomics:1972, Walter Fiersand 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 MS2coat protein. [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] :1976, Walter Fiersand his team determine the complete nucleotide-sequence of bacteriophage MS2-RNA [Fiers W et al., Complete nucleotide-sequence of bacteriophage MS2-RNA - primary and secondary structure of replicase gene, Nature, 260, 500-507, 1976] :1977 DNA is sequenced for the first time by Fred Sanger, Walter Gilbert, and Allan Maxamworking independently. Sanger's lab sequence the entire genomeof bacteriophage Φ-X174. [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] :1983 Kary Banks Mullisdiscovers the polymerase chain reactionenabling the easy amplification of DNA:1989 The humangene that encodes the CFTR protein was sequenced by 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 eukaryotegenome 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 Projectand 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]
List of sequenced eukaryotic genomes
* [http://www.mendelweb.org/MWolby.html Olby's "Mendel, Mendelism, and Genetics," at MendelWeb]
Elof Axel Carlson, "Mendel's Legacy: The Origin of Classical Genetics" (Cold Spring Harbor Laboratory Press, 2004.) ISBN 0-87969-675-3
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