6c.+History+of+DNA

media type="youtube" key="oPdrIsAbdCQ" width="425" height="350"toc media type="youtube" key="Fjgtg_YdCG0" width="425" height="350" //Students should include the researcher, important dates, a discussion of the experiment explaining the experimental design, and the impact on our understanding of DNA.//

=1866: Gregor Mendel= Gregor Mendel born in 1822. His love of nature caused him to do his experiment. Mendel’s experiment was on pea plants. He crossed smooth pea plants with wrinkly pea plants and yellow pea plants with green pea plants through pollination. In the first round he found that all the offsprings were yellow and were round. From this he concluded that yellow was dominant over green and that round was dominant over wrinkly. He was able to coin the terms dominant and recessive from this. He then crossed the offspring of his first cross with each other. He found that 75% of the pea plants yellow, 75% of the pea plants were round, 25% were green, and 25% of the plants were wrinkly. Therefore, Mendel concluded that the phenotypic ratio for a monohybrid cross, one trait, was 3:1. Mendel also determined that since there are dominant and recessive traits, some things may not show up in one generation, but may appear in the 2nd generation. He als o determined an organism must get one trait, or allele, from each parent. When Mendel did a monohybrid cross, which is two traits, he found the ratio to be 9:3:3:1 and concluded that any cross between two traits will have this phenotypic ratio. Using this experiment, Mendel was able to figure out the dominant and recessive alleles for seed shape, seed color, flower color, flower position, pod color, pod shape, and plant height. He used punnet squares to illustrate his ratios. Mendel also determined the law of segregation. He determined that online one allele can be given to an offspring by each parent. Mendel crossed a true breeding homozygous dominant plant with a true breed homozygous recessive plant. With this he got offsprings that all had purple leaves. After he did this, he crossed the generation of purple petals with each other and in this cross plants with white petals showed up. This told Mendel that the recessive allele was still there, just not expressed. The first generation proved the law of dominance, but the second generation proved the law of segregation because Mendel could now conclude that one allele came from each parent since the white flower petals were expressed in the f2 generation. Mendel called the gametes in the f1 generation heterozygous because they were carriers of the recessive allele. This part of his experiment was an example of a test cross. A test cross is when you cross an individual with a homozygous recessive parent. Mendel’s discovery of the law of independent assortment is clear in meiosis. When he performed his dihybrid cross he noticed that there were many different possible combinations for his offsprings. He noticed that the possible gametes for this cross were yellow round, yellow wrinkles, green round, and green wrinkled. After performing this cross he realized that there was not a certain order that these appeared in every time. The only thing that he could conclude was that the phenotypic ratio would be 9:3:3:1. This was an important discovery because it explained why the alleles from each parent in meiosis did not go in the same order every time. Mendel concluded that these alleles are independent of one another; therefore, they assort independently. He published his findings in 1866, but they were ignored until later around the 1900s. Thanks to Mendel, the History of genetics is unable to be questioned. We now know how to predict the offspring by just knowing information about their parents. This also showed how some of the characteristics we see on people in every day life happen. media type="youtube" key="TL-KxT5rXuM" height="315" width="420"




 * Sources **
 * Trubin, J.T. (2010). //Mendel's pea experiment//. Retrieved from [].
 * Yon Rhee, S.Y.R. (2009). //Gregor medel (1822-1884)//. Retrieved from [].
 * McClean, P.M. (2000). //Mendel's first law of genetics (law of segregation)//. Retrieved from [|http://www.ndsu.edu/pubweb/~mcclean/plsc431/mendel/mendel1.htm].

=**1911: Thomas Hunt Morgan**= T.H. Morgan was born in 1866 in Kentucky, known for being the great-grandson of Francis Scott Key, the author of the “Star Spangled Banner.” At twenty, he graduated the University of Kentucky as valedictorian, going on to major in zoology at John Hopkins University. Morgan began to study embryology at BrynMawr when his interest in the study of mutation was sparked by the rediscovery of Mendelian genetics in 1900. To research mutations in organisms, Morgan chose to follow the genetics of the //Drosophila melanogaster//, or fruit fly, in the now famous Fly Room at Columbia University. He began to crossbreed the flies to observe which mutations were passed genetically from each generation, finally witnessing the presence of a white-eyed male amongst red-eyed wild types. Specifically, Morgan studied the inheritance of vestigial wings of the Drosophila, as compared to the wild type.

Through other crosses, Morgan was able to establish in 1911 that there are sex-linked genes, traits were probably carried on sex chromosomes, and genes are carried on specific chromosomes. Furthermore, he began to pave the way for gene mapping and from his research and findings was awarded the Nobel Prize in Physiology or Medicine.

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 * Sources **
 * Kandel, E.R. (2008, November 30). thomas hunt morgan at columbia university. Retrieved from [].

=1913: Alfred Sturtevant= Alfred Sturtevant was born in Jacksonville, Illinois in 1891. When he was an undergraduate student at Columbia University, he attended a lecture by a famous scientist, Thomas Hunt Morgan. Following this lecture, Sturtevant became a student of T.H. Morgan and they began research on Drosophila flies! The idea of gene linkage came to him almost as an epiphany one night and he spent most of his undergraduate career researching this theory through the Drosophila flies. His Ph.D lecture consisted of the world’s first genetic map! It was published in 1913 and included six genes, including: eye color, wing shape, and body size, and color on the x-chromosome of the fruit fly. This map was based on the idea that these six genes did not segregate independently during meiosis. The linked genes were ordered on the x-chromosome based on the frequency with which they recombined (due to crossing-over between the two x-chromosomes in the female producing the eggs). Genes far apart on a chromosome recombine more frequently than those close together. The units of the map were the frequency of recombination between pairs of genes (Womack, 1998). From his discovery, we see that there are 100 mu on a chromosome and that we can map them by finding the distance between them.  He moved to California Institute of Technology in 1928 where he remained a biology professor there until 1951.

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 * Sources **
 * //Alfred sturtevant//. (n.d.). Retrieved from [].
 * Womack, James. (1998, March 5). //Gene mapping: origin, development, status, etc.// Retrieved from [].
 * Schaeffer, Stephen. (2009, June 11). //Chromosome Behavior and Gene Linkage//. Retrieved from [].

=**1928: Frederick Griffith**= Griffith's experiment is considered the __first demonstration of bacterial transformation__. He found that a bacterium can distinctly change its form and function which later became identified as the //transforming factor.//
 * Frederick Griffth was a British scientist whose research fosued on microbiology**, especially that of the pathology of bacterial disease. He conducted his experiments at the Ministry of Health and published his findings in the //__Journal of Hygiene__.//
 * "S" strain--lethal to mice.**
 * "R" or rough strain, which will not hurt the mouse.**


 * Heat inactivates the "S" strain.**


 * Mixing the heat-inactivated S strain with the R strain causing the mice to die; the R strain is "transformed" into a lethal form.**

The setting begins in London of 1928 when Frederick Griffith, then 49years old, found that there were two different types of the bacterium //Streptococcus pneumoniae//. He named the two types "S" and "R"--the "S" representing the SMOOTH coat strain and the "R" the ROUGH strain. When injected into mice independently and seperately, the "S" strain was discovered to be lethal while the "R" strain did not hurt the mouse whatsoever. Griffith found that he could use heat to inactivate the smooth strain. However, if he were to take a mixture of the heat-inactivated S strain, mixed with the live R strain, the bacteria would die. Thus there was some material in the heat-killed S strain that was responsible for "transforming" the live R strain into a lethal form. The R strain must have acquired live capsules of S to become lethal over many generations. The reason that Frederick Griffith's experiment is so significant is that prvious bacteriologists believed that a bacterium's form and function were "fixed." The knowledge that bacteria has the ability to change form destroys the belief that a specific strain of bacteria can be eliminated by strong competition against it. In the medical world, this is frightening because bacteria has the ability to change form/function in order to survive against medication. Furthering the work of Griffith was Oswald Avery who determined that DNA was the transforming factor.

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 * Sources **
 * //Frederick griffith's experiment//. (2003). Retrieved from []
 * //Frederick griffith//. (2010, October 31). Retrieved from [].
 * Pictures: [], []

=1941: Beadle and Tatum= //Paris....the 1930s.... // //Dr. George "Beets" Beadle and Edward Tatum, two avid geneticists, meet... // 

<span style="color: black; font-family: 'Arial Black',sans-serif; font-size: 12pt; line-height: 115%;">Dr. Beadle whisks Tatum back to his laboratory to study the relationship between DNA and enzymes. A previously proposed concept by Archibald Garrod suggested that for each enzyme, there is a specific gene that is in charge of its production. But Beadle and Tatum were not satisf <span style="font-family: 'Arial Black',sans-serif; font-size: 12pt; line-height: 115%;">ied with mere concepts...they wanted proof. And so, in 1941, they did an experiment. Their subject of choice? Bread mold, Neurospora crassa. They hypothesized that, if exposing genes to conditions that would cause mutations, each mutation would also change the function of specific enzymes in the mold. And so, being the radical scientists that they were, they exposed the mold to X-rays, causing single-gene mutations.



<span style="font-family: 'Arial Black',sans-serif; font-size: 16px; line-height: 18px;">As predicted, each of these mutations affected one specific enzyme. The result of their experiment? The popular phrase: "One gene, one enzyme." <span style="font-family: 'Arial Black',sans-serif; font-size: 16px; line-height: 18px;">media type="custom" key="7422105"media type="youtube" key="UsdIcfuXYLw" height="315" width="420" <span style="color: black; font-family: 'Arial Black',sans-serif; font-size: 12pt; line-height: 115%;">As this is interpreted today, one gene is responsible for the building of one specific enzyme.


 * Sources **
 * Evers, Chris. "The One Gene/One Enzyme Hypothesis." 3 November 2010 from @http://www.accessexcellence.org/RC/AB/BC/One_Gene_One_Enzyme.php.
 * Roberts, K. “One Gene.” 3 November 2010 from [|http://academic.pg.cc.md.us/~kroberts/biotech/chapt2/1gene.jpg].

=1944: Avery, Macleod, McCarty= // The Transforming Factor... // media type="youtube" key="u0oOyOWyMYc" height="315" width="420"

In 1944, Avery, Macleod, McCarty revisited the experiment by Griffith with genetic material transforming in strands of bacteria. Using the same strand of bacteria, S strand, Avery and his team extracted pure DNA, pure proteins and other materials from the bacterial cells. The materials were mixed with the R strand of bacteria. Rather than using mice, test tubes were used to show th e mixing of materials. After examining each mixture, only the R strand mixed with the pure DNA transformed into the S strand bacteria. Since this transformation only occurred within the pure DNA composition, implications that DNA hold genetic material were produced. Although this experiment strongly supported DNA genetic material theories, it was widely unpopular and was not accepted until the Hershey and Chase experiment in 1952. media type="custom" key="7422129"


 * Sources **
 * Oswald Theodore Avery. (2002). Retrieved November 3, 2010, from Cold Spring Harbor Laboratory website: [].
 * Ruban, J. (2010, October). DNA: The Search for the Genetic Material. Retrieved November 3, 2010, from [].

=1950: Erwin Chargaff= Erwin Chargaff was born in Czernowitz in 1905. Inspired by Avery's preceding work with genetics and DNA he began to look into the chemistry behind DNA. His experimental design consisted of only three steps; separate the DNA mixture into individual components by means of paper chromatography, convert the separated parts into mercury and salts, and then identify purines and pyrimidines by their ultraviolet absorption spectrum. Throughout the phases of his research Chargaff used the same experiment to test DNA of calf thymus, beef spleen, tubercle bacilli, and yeast. The experiments yielded the results that in double stranded DNA guanine,G units, are equal to cytosine, C units, while adenine, A units, are equal to thymine, T units. This became known as Chargraff's first rule, his second rule is that the composition of DNA varies between different organisms. His experiment and discoveries led to the eventual discovery by other scientists of the double helix shape of DNA.

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 * Sources **
 * Kresge, N, Simoni, R, & Hill, R. (2005). Chargaff's Rules: the Work of Erwin Chargaff. The Journal of Biological Chemistry, (21), Retrieved from [].
 * Pictures: [], []
 * Video: []

=** 1952: Rosalind Franklin **=

<span style="font-family: Verdana,sans-serif; line-height: 14px;">Rosalind Elise Franklin was born into at Jewish family in 1920. She was educated at a private school located in London, studying physics <span style="font-family: Verdana,sans-serif; line-height: 14px;">and chemistry. Despite the societal standards for women she went on to study at Cambridge University where she earned her Ph.D. in physical chemistry in 1945. Working at the Laboratoire Central des Services Chimiques de L’Etat, in Paris, she learned the techniques of successful x-ray crystallography. In **<span style="font-family: Verdana,sans-serif; line-height: 14px;">1952 **<span style="font-family: Verdana,sans-serif; line-height: 14px;">, at King’s College in London, after 100 hours of x-ray exposure, Franklin produced x-ray diffraction images that revealed the helical shape of DNA. The famous image provided below, **<span style="font-family: Verdana,sans-serif; line-height: 14px;">Photograph 51 **<span style="font-family: Verdana,sans-serif; line-height: 14px;">, went on to assist Watson and Crick in their further discovery of the double helix shape of DNA. Passing away at the age of 37, Rosalind Franklin’s discovery led to the understanding of the human genome. Watson and Crick used her image to produce a model of DNA that was so significant to Modern Biology that they received the Nobel Prize.

**//The Famous photograph 51 that showed the helical shape of DNA, and led to the successful model of DNA in 1962.//**

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 * Sources: **
 * //Rosalind Franklin University of Medicine and Science//. (2004). Retrieved from []
 * Pictures: [], [[[http://ensemblestudiotheatre.org/now-playing/current-productions/photograph].

=1952: Hershey-Chase Experiment= media type="youtube" key="AS3zB_ED2EE" height="300" width="545"

Michael <span style="color: black; font-family: Arial,sans-serif; font-size: 12pt; line-height: 17.75pt; margin-bottom: 0in;">Despit <span style="font-family: Arial,sans-serif; font-size: 16px; line-height: 23px;">e the name, no, is not an experiment done by the Hershey <span style="font-family: Arial,sans-serif; font-size: 16px; line-height: 23px;">Company to better their chocolate! Instead, this is a vital experiment <span style="font-family: Arial,sans-serif; font-size: 16px; line-height: 23px;">showing that DNA passes on genetic material, and not protein. First, we must know more about phage.


 * Phage **

<span style="color: black; font-family: Arial,sans-serif; font-size: 12pt;">Phage (often symboled Φ), are a type of virus that infect bacterial cells. Phage are composed of a protein shell, which houses the DNA and allows the phage to attach onto bacterial cells. They go through a process known as the lytic cycle. First in this process is adsorption, which is the process in which the bacteriophage attaches itself to the bacterial cell, and injects its DNA into the bacteria (which is also known as the penetration step). Next is replication, where the bacteria is forced to replicate the phage’s DNA. In the next stage, maturation occurs, where the various phage parts are engineered and the phage DNA is inserted into the body. Lastly is release and reinfection, which the phage burst from within the bacteria and spreads to others, starting the process over. In this cycle, however, phages are able to recombine and mix their genes with that of the host bacteria, which allows phage to have very diverse genetic codes. Those genetic codes that work live on and become new phage, those that do not die off within the bacteria. They are good examples to use for proving that DNA holds genetic material because they directly inject their DNA into bacterial cells.


 * The Experiment **

<span style="color: black; font-family: Arial,sans-serif; line-height: 17.75pt;">In the experiment, Alfred Hershey and Martha Chase used a control group of regular phage to show how the replication process occurred, which is described above. Next, they produced new generations of phage using an 35S radioactive amino acid, to change the protein label of the phage. They allowed the phage to in <span style="font-family: Arial,sans-serif; line-height: 17.75pt;">fect bacteria in a regular medium without any label. These phage that were produced were regular phage, without any sort of radioactive label, neither on the DNA nor the protein shell while the supernatant (or the leftover shell) still contained the radioactive tag. While when the DNA was stained with <span style="color: black; font-family: Arial,sans-serif; font-size: 11pt; line-height: 115%;">32 <span style="font-family: Arial,sans-serif; font-size: 11pt; line-height: 115%;">P deoxyribosenucleotides, the phage produced contained this type of DNA. This proved that DNA, not proteins, contained the genetic mate <span style="font-family: Arial,sans-serif;"> rial for life. An animation to aid in understanding: []


 * Sources **
 * <span style="color: #333333; font-family: 'times new roman',times,serif; font-size: 12px; letter-spacing: 2px; line-height: normal;">//The hershey-chase experiment//. (2009). Retrieved from http://www.accessexcellence.org/RC/VL/GG/hershey.ph
 * Hershey and chase experiment//. (2008). Retrieved from http://highered.mcgraw-hill.com/olc/dl/120076/bio21.swf//

=1953: James Watson and Francis Crick= //  Unraveling DNA's Structure... // The United Kingdom, 1952: Two students at Cambridge University narrow down the shape, form, and style of deoxyribonucleic acid, known as DNA. Their discovery, based on Rosalind Franklin's X-ray studies of DNA, revolutionized the way we understand living genetics. These men are James Watson and Francis Crick, the referred to as the "fathers of DNA." Their experimenting involved creating hundreds upon hundreds of real-life models and testing them against X-ray crystallography and density measurements.

In February of 1953, their testing ended when they determined a structurally accurate model. Later referred to by Watson as the, "...secret of life," Watson and Crick's deduction produced the model of DNA known as the "double helix", which vaguely resembles a spun ladder. The two helical chains are made up of hydrogen, oxygen, and a sugar-phosphate backbone, which represent the two siderails of the ladder. The "rungs" are specific, complementarily-paired bases that link adenine with thymine (A<span style="font-family: arial,sans-serif; font-size: small; line-height: 15px;">↔ T) and guanine with cytosine (G<span style="font-family: arial,sans-serif; font-size: small; line-height: 15px;">↔ C). The two strands run in opposite directions from the 3' (three-prime) to the 5' (five-prime) end and vice-versa. Their model also included the assertions that genetic material is the source of running and procreating information for an organism, that DNA is susceptible to mutation, and that DNA is replicated in a precise manner.

Mr. Crick was born in 1916 and died in 2004 and worked at a variety of universities and institutes prior to his death. Mr. Watson was born in 1928 and has worked at Harvard University since the mid-fifties. Their efforts, along with those of Maurice Wilkins, were awarded a Nobel Prize in Physiology and Medicine in 1962.

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 * Sources **
 * DNA Learning Center. (Producer). (2010). //Replicating the dna double helix//. [Web]. Retrived from [].
 * Cold Spring Harbor Laboratory Archive. (Photographer). (2010). //James watson and francis crick.// [Web]. Retrieved from [].
 * Nobelprize.org. (Producer). (2003). //The nobel prize in physiology or medicine 1962.// [Web]. Retrieved from [].
 * PBS. (Producer). (1998). //Watson and crick describe the nature of dna./// [Web]. Retrieved from [].
 * Pagewise. (Producer). (2002). //Francis crick & james watson: dna//. [Web]. Retrieved from [].
 * Noble, I. (2003). //'Secret of life' discovery turns 50//. BBC News. Retrieved from [].

=1956: Arthur Kornberg=

** Born on the third of March, 1918, in Brooklyn, NY, Kornberg attended City College in New York City, then earned his M.D. at the University of Rochester in 1941. Kornberg was a biochemist who was fascinated by enzymes; ** ** this led to his research on the enzymatic replication of DNA—that is, the way enzymes contribute to DNA synthesis and replication. Through his experiments, Kornberg discovered and named DNA polymerase I i **** n 1956, alongside his wife, **** Sylvy Kornberg, who was also a not **** able biochemist at the time. He wanted to learn whether or not there was a connection between “the expression of the code” and “the copying of the code” in DNA. ** ** Kornberg received a Nobel prize in 1959 for his discovery of DNA polymerase, which furthered our understanding of DNA replication. ** <span style="font-size: 14px; margin: 0px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px;"> media type="youtube" key="vn_HICkswI4?fs=1" height="385" width="480"media type="youtube" key="uMiRvcK_djU" height="315" width="420"** Sources **


 * <span style="font-family: Verdana,sans-serif; font-size: 10pt;">Kornberg, A. (1959). The biologic synthesis of deoxyribonucleic acid. Proceedings of the Nobel lecture
 * <span style="font-family: Verdana,sans-serif; font-size: 10pt;">Kresge, N., Simoni, R. D., & Hill, R. L. (n.d.). Arthur Kornberg's discovery of DNA polymerase I. Journal of Biological Chemistry, Retrieved from http://www.jbc.org/content/280/49/e46.full

=1958: Matthew Meselson and Franklin Stahl=

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Matthew Meselson and Franklin Stahl published an experiment in 1958 that changed the way DNA replication was looked at. The two scientists met at a party while attending the California Institute of Technology. When they met, Meselson was a graduate student and Stahl was a postdoctoral researcher. Their experiment on the replication of DNA helped to cement the concept of the double helix structure of DNA. The results of the Meselson-Stahl experiment contradicted with the findings of the Watson and Crick experiment, in which DNA replication was conservative. The Meselson-Stahl experiment confirmed that DNA replication was semi conservative because each daughter cell contains a strand of DNA from each parent. If DNA replication was conservative, as Watson and Crick thought, then the daughter cells would contain one with all original genetic information and one with all new genetic information. When they performed this experiment, Meselson and Stahl knew DNA replication could occur in one of three methods: semi-conservative, conservative, or dispersive. They found that DNA replication is semi-conservative because DNA replication should produce two densities; one like the first generation and one normal.

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 * Sources **
 * []
 * Davis, T.H. (2010). Meselson and Stahl: The art of DNA replication. Retrieved November 4, 2010, from Procedding of the National Academy of Sciences of the United States of America website: [].
 * DNA: Genetics experiments. (2009, September/October). Meselson-Stahl experiment. Retrieved November 4, 2010, from Wikipedia, the free encyclopedia website: [].
 * DNA is semiconservative. (2006, May 26). Meselson-Stahl experiment. Retrieved November 4, 2010, from [].
 * [].

=1968: Reiji Okazaki= __//Overview//__ Reiji Okazaki was a molecular biologist best known for his research in DNA replication. Okazaki was born 1930 in Hiroshima, Japan. He later graduated 1953 from Nagoya University and eventually worked there as a professor. He predicted (and eventually supported his theory) that synthesis on the leading strand of DNA was continuous while synthesis on the lagging strand was not. Okazaki and his wife Tsuneko preformed their experiment using E. coli in 1968. They determined that replication on the lagging strand of DNA occurred through the synthesis of polynucleotide segments that were eventually joined to create a continuous strand. These segments form because DNA polymerase can only ‘write’ in one direction. These segments came to be known as Okazaki fragments. Reiji Okazaki died not long after his profound discovery, in August 1975 at the age of 44. He died of leukemia from exposure to large amounts of radiation during the first atomic bombing of Hiroshima. His research was important because it elaborated on the Crick-Watson model, and furthered the current understanding of genetics.

__//Details of Experiment//__ In the experiment, replicating DNA was put in contact with short pulses of radioactive nucleotides and then was exposed to nonradioactive nucleotides. This is called a pulse-chase method. Afterwards, DNA was isolated and separated into individual strands in an alkaline solution. Then the alkaline solution, containing the DNA, was spun in an ultracentrifuge. An ultracentrifuge is a type of equipment that puts an object into high velocity rotation. The results were then analyzed for presence of label, and it was concluded that label occurred on two sizes-long and fragmented. There was one very long piece and the rest were merely fragments. These fragments were not broken, smaller pieces of a larger one. Instead, as Okazaki discovered, the fragments existed only temporarily and would be later incorporated into growing DNA strands by ligase enzymes. The fragments were produced as a result of DNA polymerase only being able to read correctly in one direction. Therefore, the longer piece that occurred in the results was the leading strand of DNA while the fragments were the lagging strand of DNA. Conclusively, synthesis of the leading strand is continuous while synthesis of the lagging strand is discontinuous. A step by step diagram of the experiment is linked below.

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 * Sources **
 * [].
 * []

=1979: Kary B. Mullis= media type="youtube" key="ZBwmfXKdTFU" height="315" width="420" media type="youtube" key="eEcy9k_KsDI?fs=1" height="385" width="480"

Kary B. Mullis is an American Biochemist and winner of the 1993 Nobel Prize in Chemistry for his invention of the polymerase chain reaction. Mullis received a doctorate in biochemistry at the University of California in 1973; in 1979 he joined a biotechnology firm where he completed his prize winning research. This Polymerase chain reaction allows DNA to be copied billions of times in a short amount of time. The polymerase chain reaction uses four main components: the two stranded DNA strand that is going to be copied or the template DNA, two oligonucleotide primers or short pieces of single stranded DNA that are complementary to a segment on the template DNA, nucleotides, and a polymerase enzyme that copies the template DNA by joining the free nucleotides in the correct order. These components are then heated until the template DNA is separated into two strands. When the mixture cools the primers attach to the complementary sites on the template strands. The polymerase can then copy the template strand by adding nucleotides onto the end of the primers this subsequently produces two molecules of double stranded DNA. This process can be repeated increasing the amount of DNA exponentially. This technique is applicable in medical diagnostics. It allows doctors or scientists to identify causes of infections from small samples of genetic material and it can be used to screen patients for genetic diseases and disorders such as sickle cell anemia and Huntington’s disease. PCR can also be used by biologist to identify fossil remains and forensic scientist to identify crime suspects or victims.


 * Sources **
 * Sources in a list
 * Please credit folks for info
 * Another haiku

=1975: Frederick Sanger= <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">In 1975, Frederick Sanger made a breakthrough in DNA sequencing based on Kornberg's experiments in which he devised a system called dideoxy sequencing. DNA sequencing allows the analysis of genes at the nucleotide level. A Sanger reaction consists of the following: a strand to be sequenced, DNA primers, a mixture of a particular ddNTP with its normal, and the other three dNTPs. DNA polymerase can add nucleotides only in the 5' to 3' direction, and in order to do that, there has to be a free 3' hydroxyl group (-OH) onto which it can hook the 5' end of the incoming nucleotide. ddNTPs do not have a free 3' hydroxyl group because their 3' carbon has had its oxygen atom removed. The free 3' carbon on a ddNTP has only an H. Thus, DNA polymerase cannot add any more nucleotides to a growing chain once a ddNTP has been incorporated into it.The reaction is performed four times using a different ddNTP for each reaction. When these reactions are completed, a polyacrylamide gel electrophoresis (PAGE) is performed. One reaction is loaded into one lane for a total of four lanes. The gel is transferred to a nitrocellulose filter and autoradiography is performed so that only the bands with the radioactive label on the 5' end will appear. In PAGE, the shortest fragments will migrate the farthest. Therefore, the bottom-most band indicates that its particular dideoxynucleotide was added first to the labeled primer. Therefore, ddATP must have been added first to the primer, and its complementary base, thymine, must have been the base present on the 3' end of the sequenced strand. One can continue reading in this fashion. The sequenced strand can be read 5' to 3' by reading top to bottom the bases complementary to the those on the gel. Sanger’s innovation was basically the discovery of the ddNTP’s role in ending the sequence because of their lack of a –OH group on the 3’ direction.media type="youtube" key="VxM6GsBlj0M" height="315" width="420"

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Edwin Southern <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">media type="youtube" key="oPdrIsAbdCQ" width="425" height="350"

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Eric Lander media type="youtube" key="Fjgtg_YdCG0" height="315" width="420"

Craig J. Venter media type="youtube" key="gU7I9JqIUso" height="300" width="434"