Editing Genetics (section)

=== Molecular genetics ===
{{Main|Molecular genetics}}
[[File:DNA Overview2.png|thumb|upright=0.6|[[DNA]], the molecular basis for [[Heredity|biological inheritance]]. Each strand of DNA is a chain of [[nucleotide]]s, matching each other in the center to form what look like rungs on a twisted ladder.]]

Although genes were known to exist on chromosomes, chromosomes are composed of both [[protein]] and DNA, and scientists did not know which of the two is responsible for inheritance. [[Griffith's experiment|In 1928]], [[Frederick Griffith]] discovered the phenomenon of [[Transformation (genetics)|transformation]]: dead bacteria could transfer [[genetic material]] to "transform" other still-living bacteria. Sixteen years later, in 1944, the [[Avery–MacLeod–McCarty experiment]] identified DNA as the molecule responsible for transformation.<ref name=Avery_et_al>{{cite journal | vauthors = Avery OT, Macleod CM, McCarty M | 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 = The Journal of Experimental Medicine | volume = 79 | issue = 2 | pages = 137–158 | date = February 1944 | pmid = 19871359 | pmc = 2135445 | doi = 10.1084/jem.79.2.137 }} Reprint: {{cite journal | vauthors = Avery OT, MacLeod CM, McCarty M | title = Studies on the chemical nature of the substance inducing transformation of pneumococcal types. Inductions of transformation by a desoxyribonucleic acid fraction isolated from pneumococcus type III | journal = The Journal of Experimental Medicine | volume = 149 | issue = 2 | pages = 297–326 | date = February 1979 | pmid = 33226 | pmc = 2184805 | doi = 10.1084/jem.149.2.297 }}</ref> The role of the nucleus as the repository of genetic information in eukaryotes had been established by [[Joachim Hämmerling|Hämmerling]] in 1943 in his work on the single celled alga ''[[Acetabularia]]''.<ref>{{cite book |title=Cell and Molecular Biology | vauthors = Khanna P |publisher=I.K. International Pvt Ltd |date=2008 |page=221 |isbn=978-81-89866-59-4 }}</ref> The [[Hershey–Chase experiment]] in 1952 confirmed that DNA (rather than protein) is the genetic material of the viruses that infect bacteria, providing further evidence that DNA is the molecule responsible for inheritance.<ref>{{cite journal | vauthors = Hershey AD, Chase M | title = Independent functions of viral protein and nucleic acid in growth of bacteriophage | journal = The Journal of General Physiology | volume = 36 | issue = 1 | pages = 39–56 | date = May 1952 | pmid = 12981234 | pmc = 2147348 | doi = 10.1085/jgp.36.1.39 }}</ref>

[[James Watson]] and [[Francis Crick]] determined the structure of DNA in 1953, using the [[X-ray crystallography]] work of [[Rosalind Franklin]] and [[Maurice Wilkins]] that indicated DNA has a [[Helix|helical]] structure (i.e., shaped like a corkscrew).<ref>{{cite book |title=The Eighth Day of Creation: Makers of the Revolution in Biology | vauthors = Judson H |author-link=Horace Freeland Judson |year=1979 |publisher=Cold Spring Harbor Laboratory Press |isbn=978-0-87969-477-7 |pages=51–169}}</ref><ref name=watsoncrick_1953a>{{cite journal | vauthors = Watson JD, Crick FH | title = Molecular structure of nucleic acids; a structure for deoxyribose nucleic acid | journal = Nature | volume = 171 | issue = 4356 | pages = 737–738 | date = April 1953 | pmid = 13054692 | doi = 10.1038/171737a0 | url = http://www.nature.com/nature/dna50/watsoncrick.pdf | url-status = live | s2cid = 4253007 | df = dmy-all | bibcode = 1953Natur.171..737W | archive-url = https://web.archive.org/web/20070204110320/http://www.nature.com/nature/dna50/watsoncrick.pdf | archive-date = 4 February 2007 }}</ref> Their double-helix model had two strands of DNA with the nucleotides pointing inward, each matching a complementary nucleotide on the other strand to form what look like rungs on a twisted ladder.<ref name=watsoncrick_1953b>{{cite journal | vauthors = Watson JD, Crick FH | title = Genetical implications of the structure of deoxyribonucleic acid | journal = Nature | volume = 171 | issue = 4361 | pages = 964–967 | date = May 1953 | pmid = 13063483 | doi = 10.1038/171964b0 | url = http://www.nature.com/nature/dna50/watsoncrick2.pdf | url-status = live | s2cid = 4256010 | df = dmy-all | bibcode = 1953Natur.171..964W | archive-url = https://web.archive.org/web/20030621051153/http://www.nature.com/nature/dna50/watsoncrick2.pdf | archive-date = 21 June 2003 }}</ref> This structure showed that genetic information exists in the sequence of nucleotides on each strand of DNA. The structure also suggested a simple method for [[DNA replication|replication]]: if the strands are separated, new partner strands can be reconstructed for each based on the sequence of the old strand. This property is what gives DNA its semi-conservative nature where one strand of new DNA is from an original parent strand.<ref>{{cite journal | vauthors = Stratmann SA, van Oijen AM | title = DNA replication at the single-molecule level | journal = Chemical Society Reviews | volume = 43 | issue = 4 | pages = 1201–1220 | date = February 2014 | pmid = 24395040 | doi = 10.1039/c3cs60391a | url = https://pure.rug.nl/ws/files/14412201/2014ChemSocRevStratmann.pdf | url-status = live | s2cid = 205856075 | archive-url = https://web.archive.org/web/20170706055534/https://pure.rug.nl/ws/files/14412201/2014ChemSocRevStratmann.pdf | archive-date = 2017-07-06 }}</ref>

Although the structure of DNA showed how inheritance works, it was still not known how DNA influences the behavior of cells. In the following years, scientists tried to understand how DNA controls the process of [[Protein biosynthesis|protein production]].<ref name="Betz2010">{{cite book |vauthors = Frederick B |title=Managing Science: Methodology and Organization of Research |url=https://books.google.com/books?id=1ARRexcXgAgC&pg=PA76 |year=2010 |publisher=Springer |isbn=978-1-4419-7488-4 |page=76}}</ref> It was discovered that the cell uses DNA as a template to create matching [[messenger RNA]], molecules with [[nucleotide]]s very similar to DNA. The nucleotide sequence of a messenger RNA is used to create an [[amino acid]] sequence in protein; this translation between nucleotide sequences and amino acid sequences is known as the [[genetic code]].<ref name="Rice2009">{{cite book | vauthors = Rice SA |title=Encyclopedia of Evolution |url=https://books.google.com/books?id=YRcAVvmE6eMC&pg=PA134 |year=2009 |publisher=Infobase Publishing |isbn=978-1-4381-1005-9 |page=134}}</ref>

With the newfound molecular understanding of inheritance came an explosion of research.<ref name="Sarkar1998">{{cite book | vauthors = Sarkar S |title=Genetics and Reductionism |url=https://books.google.com/books?id=7lzpDHFw-40C&pg=PA140 |year=1998 |publisher=Cambridge University Press |isbn=978-0-521-63713-8 |page=140}}</ref> A notable theory arose from [[Tomoko Ohta]] in 1973 with her amendment to the [[neutral theory of molecular evolution]] through publishing the [[nearly neutral theory of molecular evolution]]. In this theory, Ohta stressed the importance of natural selection and the environment to the rate at which genetic [[evolution]] occurs.<ref>{{cite journal | vauthors = Ohta T | title = Slightly deleterious mutant substitutions in evolution | journal = Nature | volume = 246 | issue = 5428 | pages = 96–98 | date = November 1973 | pmid = 4585855 | doi = 10.1038/246096a0 | s2cid = 4226804 | bibcode = 1973Natur.246...96O }}</ref> One important development was chain-termination [[DNA sequencing]] in 1977 by [[Frederick Sanger]]. This technology allows scientists to read the nucleotide sequence of a DNA molecule.<ref name=sanger_et_al>{{cite journal | vauthors = Sanger F, Nicklen S, Coulson AR | title = DNA sequencing with chain-terminating inhibitors | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 74 | issue = 12 | pages = 5463–5467 | date = December 1977 | pmid = 271968 | pmc = 431765 | doi = 10.1073/pnas.74.12.5463 | doi-access = free | bibcode = 1977PNAS...74.5463S }}</ref> In 1983, [[Kary Banks Mullis]] developed the [[polymerase chain reaction]], providing a quick way to isolate and amplify a specific section of DNA from a mixture.<ref name=saiki_et_al>{{cite journal | vauthors = Saiki RK, Scharf S, Faloona F, Mullis KB, Horn GT, Erlich HA, Arnheim N | title = Enzymatic amplification of beta-globin genomic sequences and restriction site analysis for diagnosis of sickle cell anemia | journal = Science | volume = 230 | issue = 4732 | pages = 1350–1354 | date = December 1985 | pmid = 2999980 | doi = 10.1126/science.2999980 | bibcode = 1985Sci...230.1350S }}</ref> The efforts of the [[Human Genome Project]], Department of Energy, NIH, and parallel private efforts by [[Celera Genomics]] led to the sequencing of the [[human genome]] in 2003.<ref name=human_genome_project /><ref>{{Cite journal|title=The sequence of the human genome|journal=Science|volume=291}}</ref>