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Viral Vector

SIGNIFICANCE

Double Helix Model of DNA

TOP TEN

Watson and Crick’s model of DNA proved to be the correct model of DNA because it satisfied various criteria that the DNA molecule had to have in order to be regarded as the genetic material of all organisms. The model also taught scientists new things about how DNA contains life’s genetic information and how it can replicate itself during DNA replication. Watson and Crick also clarified doubts about how such a simple molecule can carry so much information; they stated that it is not the number of different nucleotides found in the molecule, but rather the varying sequences of the nucleotide base-pairs that makes up the varying genes found in different organisms. The idea of the two backbones running in opposite directions explains how DNA can replicate itself through semiconservative replication. Each of the two new DNA molecules formed in replication contain both a parent strand and a new complementary daughter strand. This gave scientists the understanding of how DNA replication can be so accurate and how genetic information can be passed down to offspring, as well as how mutations can occur can occur during replication.

In the early 1950s, James Watson and Francis Crick were competing in a race against other scientists to determine the correct structure of DNA. After an incorrect model had been announced by another scientist Linus Pauling, who suggested a triple helix model with the nucleotide bases on the outside, Watson and Crick were prompted to try and beat Pauling and find the correct model. After viewing the X-ray diffraction patterns of Wilkins and Franklin’s experiments and taking a closer look at Erwin Chargaff’s observations of nucleotide base ratios in various organisms, Watson and Crick concluded that the DNA molecule was a double helix of two sugar-phosphate backbones running in opposite directions and the nitrogenous bases paired as adenine-thymine and cytosine-guanine on the inside of the double-helix. This model satisfied all traits of DNA and is still the same one that scientists use today to classify DNA.

1988

Genetically Modified Organism (GMO)

Matthew Meselson and Franklin Stahl

Restriction Enzyme

Gel Electrophoresis

1958

1973

Double Helix Model of DNA

1968

Tools commonly used by molecular biologists to deliver genetic material into cells; Viruses have evolved specialized molecular mechanisms to efficiently transport their genomes inside the cells they infect - first implemented by Stephen Rosenberg - successfully inserted foreign genes into humans using viral vectors.

1951

1953

Cut DNA at a specific nucleotide sequence in order to insert genes into plasmids isolated from bacteria

Demonstrate that DNA replicates semiconservatively: each strand from the parent DNA molecule ends up paired with a new strand from the daughter generation.

Organisms that contain DNA that has been modified, usually using recombinant DNA technology, or that was derived from other species; the first GMO was made by Herbert Boyer and Stanley Cohen when they transformed bacteria by adding an antibiotic resistance gene to the bacteria.

A technique used to separate a mixture of DNA pieces using DNA probes, which are single-stranded pieces of synthetic DNA that can base-pair with specific DNA fragments in the sample of a given STR, which is a small, repeating segment of DNA that can be used to identify people with astonishing accuracy; the pattern produced by running DNA samples on STR gels is the DNA profile

James Watson and Francis Crick; Described the double helix model of DNA and correct base pairing of the nucleotides (adenine - thymine and cytosine - guanine)

https://www.sciencehistory.org/historical-profile/james-watson-francis-crick-maurice-wilkins-and-rosalind-franklin

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Polymerase Chain Reaction (PCR)

Human Genome Project

SIGNIFICANCE

TOP TEN

Before the 1986, copying selected pieces of DNA could take up to 3 weeks by hand and 8 hours by machine. It was useful to make and analyze copies of DNA for sequencing, forensic purposes, and DNA-based diagnostics, but the pre-PCR process was painstakingly slow. Kary Mullis had earned a doctorate in biochemistry and by 1979 was working for the Cetus corporation as a DNA chemist. He was in charge research on the synthesis of oligonucleotides (short DNA sequences of up to twenty nucleotide bases). He was trying to find a way to detect point mutations but struggled because DNA pieces were too long and primers would almost never bond in the right spot. He needed a way to increase the amount of specific genes. While driving his Honda Civic on Highway 128 from San Francisco to Mendocino, Mullis realized that if two opposing primers were adding between separated DNA strands, then two copies of the DNA fragment could be made in one cycle. Then the two pieces could each produce two more pieces and so on. The cycle consists of denaturalization, annealing, and elongation. At first, DNA polymerase would be denatured in every cycle due to heat. Mullis soon found a version of DNA polymerase in the extremophilic bacteria Thermophilus aquaticus that could still perform at higher temperatures so it would not have to be replaced after every cycle. PCR starts with a small test tube containing DNA, primers, free nucleotides, and the special DNA polymerase. PCR involves the following steps:

1. The test tube is heated to 194℉ to 203℉. The high temperatures break the hydrogen bonds between complementary bases, separating the DNA into single strands.

2. The temperature is lowered to about 122℉, which allows the two primers to form complementary base pairs with the original DNA strands.

3. The temperature is raised to 158℉ to 162℉. DNA polymerase uses the free nucleotides to make copies of the DNA segment bounded by the primers.

4. This cycle is repeated, usually 30 to 40 times, until the reactants have been used up.

The discovery of PCR now allows scientists to produce an almost unlimited amount of highly purified DNA molecules which can further be analyzed or manipulated. This discovery PCR has allowed for almost every biotechnology within the past 20 years to be possible. PCR aids in the creation of DNA profiles and with the process of DNA fingerprinting. The Department of Justice in the U.S. has established a set of 13 STRs, or short segments of DNA, to be used to identify people. PCR can created millions of copies of a person’s STRs. Only they will have this combination. Paternity tests are possible and criminals can be easily identified if DNA is available for analysis. Making copies makes it easier to examine and sequence DNA. DNA can be examined by more people and easier if there are more copies available. This means that genetic diseases can be identified quicker than symptoms can show. PCR also makes it easier to create transgenic organisms and to transplant properly functioning genes. PCR has made DNA more accessible for all kinds of research on genetics and new biotechnology.

There are 4 main reasons why scientists would want to know the nucleotide sequence of all the DNA in our entire set of genes. First, the function of genes could be determined. Scientists can use the genetic code to predict the amino acid sequence of the protein that a gene codes for. They can compare these proteins to proteins with known functions to find out what a gene does. Second, the information contained in the complete nucleotide sequences of genes has allowed more diseases to be associated with specific genes. Third, human genomes are not all the same. Most DNA is the same, but alleles can vary which can cause different traits as well as diseases. Researchers can sequence more genomes and compare them to determine the mutations that cause diseases. If the disease-causing mutation is known, then a treatment can be easier to find (if there is one). Specific human genomes can also lead to personalized treatment for diseases based on how each body will respond to the treatment. Finally, the Human Genome Project helps to put our place in the evolutionary chain. Comparing genomes to other species can help biologists determine what makes us human. The Human Genome Project released its information to the public almost immediately. In recent years, companies have emerged that specialize in gene sequencing. They can allow anyone with the proper financial resources to get their genome sequenced. This can help a person see all the possibilities of diseases/conditions they could develop in the future. The full effect of the Human Genome Project can not be seen today, but the results add to our knowledge and sequencing genomes has only gotten faster and more accessible.

The Human Genome project was initiated in 1900 by the National Institutes of Health and the U.S. Department of Energy as well as universities across the United States and international partners in the United Kingdom, France, Germany, Japan, and China. Across the world, geneticists had one goal, to sequence the entire human genome. At that point, DNA could be copied easily with PCR, genes could be altered and reinserted into organisms, and the genomes of simpler organisms had been sequenced, but sequencing the human genome was a daunting task. Human contain more chromosomes than the organisms with sequenced genomes, making the project much more complex. The initial plan was for the project to be complete by 2005, yet a draft was produced in 2001 and the final genome was produced in 2003. Sequencing has to occur in small segments of DNA due to the amount of raw information. The physical map of the human genome had already been determined and served as a guide for sequencing. The process of sequencing usually involved the labeling of bases and merging of cloned DNA to observe the order of bases. Three main pieces of information that had been discovered by the end of the project were:

  • There are approximately 22,300 protein-coding genes in human beings
  • The human genome has significantly more segmental duplications (nearly identical, repeated sections of DNA) than had been previously suspected.
  • At the time when the draft sequence was published fewer than 7% of protein families appeared to be vertebrate specific

Microarray/Diagnostic Array

Restriction Fragment Length Polymorphism

Dolly the Sheep

Polymerase Chain Reaction (PCR)

Completion of the Human Genome Project

mRNA is the Intermediate Between DNA and Protein

SIGNIFICANCE

TOP TEN

By the late 1950s, scientists had discovered a molecule known as RNA known as ribonucleic acid that was presumed to take part in protein synthesis. But they did not know for sure how it worked or exactly what role it played in protein synthesis. Sydney Brenner, Francois Jacob, and Matthew Meselson knew based on the structure of the eukaryotic cell that DNA alone could not supplement for initiating protein synthesis. Therefore, they hypothesized that RNA may be an intermediate information carrier between DNA in the nucleus and ribosomes in the cytoplasm. At the time, scientists had thought that there was a single ribosome that is synthesized for every gene that codes for a single enzyme. But this was fundamentally wrong as there are not nearly enough ribosomebeing produced fast enough for the rate at which proteins were being synthesized. Brenner, Jacob, and Meselson conducted an experiment to isolate RNA to study it further, and they concluded from their research that supported their hypothesis - that RNA was a copy of the information in DNA. As a messenger, RNA transported the information from the nucleus to the protein-making machinery in the cell.

Brenner, Jacob, and Meselson’s results revolutionized the world’s perception of the process of protein synthesis. They discovered a vital intermediate molecule (RNA) and its structure, which helped future scientists better understand exactly how DNA is transcribed and translated into amino acids that make up proteins. The discovery of various types of RNA (mRNA, tRNA, and rRNA) shed light on the structure and organization of the ribosome, which, at the time, was still a fairly new and unexplored aspect of protein synthesis. Scientists were also able to better understand the amino acid code, and how mRNA and tRNA form amino acids from simple three base-pair sequences of nucleotides. And, just like the discoveries of other scientists, their experiment gave future scientists a better understanding of how the cell organizes and controls protein synthesis, along with how mutations can be expressed through protein synthesis if there are errors in RNA transcription and the genes are translated incorrectly to form incomplete or incorrect proteins.

Father of Genetics

Transformation in Genetics

SIGNIFICANCE

Chromosome Movement in Mitosis

SIGNIFICANCE

One Gene, One Protein

1988

SIGNIFICANCE

Gregor Mendel was the first geneticist to discover the common patterns of inheritance and many essential facts about genes, allele, and how alleles in gametes and zygotes distribute during sexual reproduction. The design of his experiments were simple. He used the edible pea plant to conduct experiments of inheritance. He found that when he cross-fertilized pea plants with different true-breeding traits, he found that one trait would be dominant over the other. He also crossed plants with multiple different traits. From his experiments, he found that when true-breeding plants cross, the F1 generation will all show the dominant trait, but in the F2 generation about one in four will show the recessive trait. When crossing a true-breeding plant for two dominant traits with a true-breeding plant for two recessive traits, the ratio of types of F2 offspring is a 9:3:3:1 (both dominant traits : one dominant and one recessive trait : the other dominant and other recessive trait : both recessive trait).

Law of Independent Assortment: the independent inheritance of two or more traits, assuming that each trait is controlled by a single gene with no influence from gene(s) controlling the other trait; states that the alleles of each gene are distributed to the gametes independently of the alleles for other genes; this law is true only for gene located on different chromosomes or very far apart on a single chromosome.

1996

TOP TEN

Mendel’s experiments along with current knowledge of genes create the 5-part hypothesis of the inheritance of single traits:

  • Traits are determined by genes and each organism has two versions, or alleles of a gene located on homologous pairs of chromosomes.
  • Dominant alleles mask the presence of recessive alleles, but an organism can still have both.
  • Law of Segregation: The principle that each gamete receives only one of each parent’s pair of alleles of each gene.
  • Because homologous chromosomes separate at random during meiosis, chance determines which allele a gamete receives
  • True-breeding organisms have two copies of the same allele for a given gene and are considered homozygous for that trait. Hybrid organism contain two different alleles for a given gene and are considered heterozygous for that trait.

Mendel’s results were published in 1865, but went unnoticed in the field of biology during his lifetime. Mendel knew nothing of the physical nature of genes or chromosomes, but was still able to determine the basics of how traits are inherited. His experiments serve as the base for all other genetic discoveries.

Viruses Alter DNA and Not Proteins

TOP TEN

Flemming laid out all of the steps of mitosis that set the framework for studies of when and how cells divide their chromosomes evenly among their daughter cells during cell division. If it was not for his studies, scientists would not have clearly understood sexual reproduction, or meiosis, and how chromosomes could cross over and independently assort between daughter cells and produce genetically unique organisms. Flemming also allowed future scientists to better understand how chromosomes are structured and how DNA is able to replicate and divide in an organized manner by condensing into homologues. His work helped to put Mendel’s work on heredity in pea plants in a physical perspective and prove how traits can be passed down independently to daughter cells on a molecular level. This has allowed scientists today to understand how mutations can occur during chromosomal replication and has set the foundation for research into causes and treatment for genetic disorders.

Walther Flemming was a German anatomist and a founder of the science of cytogenetics, or the study of the cell’s hereditary material - the chromosomes. He was one of the earliest scientists to use aniline dyes to identify and visualize cell structures, and he discovered a certain combination of dyes that revealed a thread-like material found in the cell, or the chromosomal DNA. By applying these dyes to cell killed at different stages of cell division, Flemming was able to clearly establish the sequence of changes occurring in the nucleus during cell division. He observed that the threads (chromosomes) shortened and split longitudinally in halves, each half moving to opposite sides of the cell. He labelled the entire process as mitosis and published his work in 1882, but his work was not recognized until 20 years later, when Gregor Mendel’s studies resurfaced and Flemming’s discoveries justified Mendel’s hypotheses.

In the late 1920s, Frederick Griffith, a british researcher, was trying to make a vaccine to prevent bacterial pneumonia, which was a major cause of death at the time. He obtained two strains of the Streptococcus pneumoniae bacterium, an R-strain, which did not cause pneumonia, and an S-strain, which did cause pneumonia. Using mice for his experiment, he conducted a series of four experiments to try and determine a vaccine for pneumonia. For the first experiment, he injected live R-strain in to the mice, and found that the mice survived and was healthy. For the second experiment, he injected live S-strain into the mice, and found that the mice contracted pneumonia and died. In the third experiment, he injected heat-killed S-strain bacteria into the mice and found that the mice remained healthy. Then, he combined both live R-strain and heat-killed S-strain, seeing as neither of them alone were pathogenic, and injected them in to the mice. He found that the mice contracted pneumonia and died. This meant that the S-strain bacteria transformed the R-strain bacteria into deadly S-strain bacteria by passing on its genes. This discovery showed that genes could not be found in the proteins, as they would have denatured when the S-strain were killed by the heat. Therefore, genetic information had to be in the DNA, as it would have remained intact even after the S-strain bacteria was killed by the heat.

SIGNIFICANCE

By the late 1800s, scientists had learned that genetic information exists in subunits called genes. However, they thought that genes were made up of proteins in the cells, and not in the DNA. It made more sense, as proteins were in much higher abundance and came in a variety of shapes and sizes, while DNA was very small and had a relatively basic structure of repeating nucleotides, with the only variation being with the four different bases. It was Griffith’s accidental discovery that altered the perception of the world today and led scientists in the right direction - that genetic information was found in the varied sequences of DNA nucleotides and not in the proteins. Today, scientists are mapping DNA sequences and understanding more about genetic diseases than ever before, and they would not have even known where to look if it was not for Griffith and his pneumonia experiment.

2003

TOP TEN

George Beadle and Edward Tatum were geneticists that used the metabolic pathways of a common bread mold, Neurospora crassa, to study the synthesis of proteins from genes. They induced mutations by exposing Neurospora to X-rays, and then studied the inheritance of the metabolic pathway that synthesizes the amino acid arginine. In normal molds, arginine is synthesized by enzyme 2 (synthesized from gene A) from citrulline, which is in turn synthesized by enzyme 1 (synthesized from gene B) from ornithine. Normal Neurospora molds can synthesize arginine, citrulline, and ornithine. Mutant A can only grow if arginine is added. It cannot synthesize arginine from citrulline or ornithine because it has a defect in enzyme 2. Mutant B can only grow if either arginine or citrulline is added. It cannot synthesize arginine because it has a defect in enzyme 1. By analyzing which supplements allowed mutant molds to grow on simple nutrient medium, Beadle and Tatum concluded that a single gene codes for the synthesis of a single enzyme.

Beadle and Tatum’s experiment served to help future scientists to understand how the cell transcribes its genetic information into RNA and then translates RNA into protein. It showcased that only a single gene is necessary for the synthesis of a single protein. Their research set the groundwork for further research that explained how each sequence of DNA (gene) is translated into a single protein. Further studies that showed how introns are spliced from DNA sequences and how exons are attached together were more clearly understood with the “one gene, one protein” conclusion from Beadle and Tatum’s research. Their experiment also provided a better idea of how coding for proteins are organized and how cells can ensure to translate entire proteins by simply transcribing entire genes. This, in turn, set the framework for understanding how proteins form many of the cell’s cellular structures and the enzymes that catalyze its chemical reactions through a controlled flow of information from DNA to protein.

1986

TOP TEN

In the early twentieth century, many biologists were convinced that genetic information was stored in proteins to their variety of shapes and functions. In 1944, the Avery-MacLeod-McCarty experiments were published and concluded that when proteins are destroyed, transformation can still occur. Yet, scientists were still skeptical. In the early 1950s, Alfred Hershey and Martha Chase were determined to use bacteriophages to determine the substance that carries genetic information. Bacteriophages are viruses that only infect bacteria. Their structure consists of only an outer coat and genetic material inside. They are chemically simple, only being composed of proteins and DNA. Phages insert genetic material into bacteria so if Hershey and Chase could determine what made up the coat and inner material, they would know what molecule carries genetic information. They labeled the protein of one population of phages with radioactive sulfur and labeled the DNA of another population with radioactive phosphorus. Both chemical labels are found in one biological molecule, but not the other. They infected bacteria with the labeled phages and used a blender to break off the phage coats. Then, they used a centrifuge to separate the phage coats and bacteria and tested each for radioactivity. When they tested the population with labeled DNA, the bacteria were also radioactive. When they tested the population with labeled protein, the coats were radioactive, but the bacteria were not. This proved that the hereditary molecule is made of DNA, not protein.

1980

Hershey and Chase confirmed that DNA is the hereditary molecule. This prompted further research on how DNA carries genetic information. Biologists could stop focusing on proteins and shift focus to the structure, patterns, and sequence of DNA as genetic material. This discovery helped form a path for scientists to determine the details of Mendelian inheritance and how the chemical makeup of genetic material allowed for traits to the behave that way.

Chorionic Villus Sampling (CVS)

J. L. Alloway

Joe Hin Tjio

First Animal Gene Cloned

http://www.frontlinegenomics.com/opinion/5005/time-play-synth/

Amniocentesis

Gregor Mendel

Sydney Brenner, François Jacob and Matthew Meselson

Walther Flemming

Charles Darwin

Frederick Griffith

George Beadle and Edward Tatum

1968

1973

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Alfred Hershey and Martha Chase

1955

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The first mammal to be cloned successfully from an adult somatic cell by nuclear transfer. She lived for 6 and a half years and proved that genes from the nucleus of a somatic cell are able to revert back to the embryonic phase and a new organism can form.

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Developed by Kary Mullis of the Cetus Corporation; Can be used to amplify and make billions/ trillions of copies of selected pieces of DNA; consists of a cycle of heating, cooling, and warming that is repeated 30 to 40 times

This project began in 1990 and aimed to determine the nucleotide sequence of all the DNA in our entire set genes, called the human genome. In April 2003, the human genome was sequenced with an accuracy of about 99.99%.

A grid of DNA segments of known sequence that is used to test and map DNA fragments, antibodies, or proteins - first application was in 1995 and was used for gene expression analysis and genotyping

1952

A variation in the length of restriction fragments produced by a given restriction enzyme in a sample of DNA; such variation is used in forensic investigations and to map hereditary disease; developed in 1980 by Botstein

Prenatal test in which a sample of chorionic villi is removed from the placenta for genetic testing of the baby

http://slideplayer.com/slide/8635612/

https://en.wikipedia.org/wiki/Polymerase_chain_reaction

Followed the discovery that cultured amniotic fluid cells could be used to obtain fetal karyotype and can be used for genetic diagnosis of the fetus.

Researchers fuse a segment of DNA containing a gene from the African clawed frog Xenopus with DNA from the bacterium E. coli and placed the resulting DNA back into an E. coli cell; there, the frog DNA was copied and the gene it contained directed the production of a specific frog protein.

Discovered that the mice played no role in transformation, which occurred just as well when live R-strain bacteria were mixed with dead S-strain bacteria in culture dishes - proved that mice had nothing to do with it and the transformation occurred solely because of the DNA.

Discovered natural selection and wrote “On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life.”

Defines 46 as the exact number of chromosomes in human cells; foundation for our understanding of how certain diseases occur due to mutations on certain chromosomes only

Describes chromosome behavior during animal cell division. He stains chromosomes to observe them clearly and describes the whole process of mitosis in 1882

Discovered that heredity is transmitted in units. His experiments on peas demonstrate that heredity is transmitted in discrete units. The understanding that genes remain distinct entities even if the characteristics of parents appear to blend in their children explains how natural selection could work and provides support for Darwin’s proposal.

Showed that even when dead, S-strain bacteria (pathogenic) can transform R-strain bacteria (pathogenic) into disease-causing bacteria, proving genetic information is in DNA and not protein

Discovered that mRNA takes information from DNA in the nucleus to the protein-making machinery in the cytoplasm

Conducted experiments on Neurospora crassa that showed that genes act by regulating distinct chemical events and proposed that each gene directs the formation of one enzyme

Showed that only the DNA of a virus needs to enter a bacterium to infect it, providing strong support for the idea that genes are made of DNA

http://genoma.com/blog/en/mendelian-genetics-gregor-mendel-to-predictive-medicine/

https://norkinvirology.wordpress.com/2016/10/06/a-most-elegant-experiment-sydney-brenner-frjacob-mathew-meselson-and-the-discovery-of-messenger-rna/

https://hersheychasednaexperiment.weebly.com/basic-experimental-overview.html

https://en.wikipedia.org/wiki/Walther_Flemming

https://simple.wikipedia.org/wiki/Griffith%27s_experiment

SIGNIFICANCE

X-ray Diffraction of DNA

First Human Genetic Map

TOP TEN

After earning a degree in chemistry, Rosalind Franklin arrived to King’s College in 1951 for a fellowship to investigate x-ray diffraction studies of proteins in solution. The focus of her fellowship changed when the assistant director of Randall's lab, Maurice Wilkins began working with an unusually pure sample of DNA. Wilkins suggested to the head of the biophysics program that Franklin’s expertise would be better spent investigating DNA. Franklin was contacted via letter of this change, but Wilkins was not aware of the letter’s content and Franklin was not aware of Wilkin’s interest in the project. For this reason, Franklin believed she would be leading the research on her own. This led to tension between the two. After obtaining larger quantities of pure DNA, Wilkins determined that it could be drawn out into very thin, uniform fibers like a spider web. This suggested to him a regular structure that might yield an x-ray diffraction pattern. Wilkins and his partner Raymond Gosling took photos of the DNA at varying humidity levels. Some were blurry but some showed the typical diffraction pattern of a molecule in a helical shape. Franklin developed her own x-ray equipment and found the same results along with the discovery of two forms of DNA. Franklin and Wilkins reached a compromise: Franklin would focus on the A type (dry, crystallized form) and Wilkins would focus on the B type (longer, thinner, heavily hydrated "paracrystalline" form). Both struggled to get consistent resulted of the helical diffraction pattern, but by the end of Franklin's fellowship, they extracted three main pieces of information about DNA:

  • Molecule of DNA is long and thin, with a uniform diameter of two nanometers
  • DNA is helical
  • DNA consists of repeating subunits

Because of the bad relationship between Franklin and Wilkins, research and findings came slowly. They worked separately and would have been faster if they had been able to work together. Nevertheless, the two found that DNA is a uniform diameter, helical, and consists of repeating subunits. They were not able to work out the structure of DNA, but James Watson and Francis Crick were able to use their information to make their model. They knew how complex organic molecules bonded to each other and had intuitions that biological molecule tend to come in pairs if they are important. Franklin and Wilkins reached some great findings, but could not complete an accurate model of DNA before their competitors. Despite this, their research helped lead to the correct model which lead to DNA sequencing and the discovery that DNA codes for proteins. Rosalind Franklin was also one of few women making major scientific discoveries in the field of science at the time, proving that women had a place in the laboratory.

Frederick Miescher

Erwin Chargaff

Oswald Avery, Colin Macleod, and Maclyn McCarty

1987

RNA Interference

Maurice Wilkins and Rosalind Franklin

1869

Marshall Nirenberg

2006

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Based on variations in DNA sequence that can be observed by digesting DNA with restriction enzymes; can be used to help locate genes responsible for diseases.

1966

Isolates DNA from cells for the first time and calls it “nuclein”. Provided the foundation for DNA research and investigation from outside of the cell.

A biological process in which RNA molecules inhibit gene expression or translation, by neutralizing targeted mRNA molecules; discovered by Andrew Z. Fire and Craig C. Mello.

Measured the amount of each of the 4 bases in various different organisms and found that adenine and thymine were always present in the same ratios, and cytosine and guanine were always present in the same ratios

Shot X-rays at DNA and measured the diffraction patterns; discovered 3 things - DNA is long and thin (about 2 nm wide), consists of repeating subunits, and is helical (shaped like a corkscrew)

Discovered that the transforming molecule is DNA and not traces of protein contaminating the DNA; treated some samples of R-strain and killed S-strain with protein-destroying enzymes and some with DNA-destroying enzymes; only the samples treated with DNA-destroying enzymes prevented transformation

Figure out the genetic code that allows nucleic acids with their 4 letter alphabet to determine the order of 20 kinds of amino acids in proteins

https://en.wikipedia.org/wiki/Photo_51

Great Genetics Discoveries

CITATIONS

“All About The Human Genome Project (HGP).” National Human Genome Research Institution, NIH, www.genome.gov/10001772/all-about-

the--human-genome-project-hgp/.

Audesirk, Teresa, et al. Biology: Life on Earth. Ninth ed., Pearson, 2011.

Bouard, D, et al. “Viral Vectors: from Virology to Transgene Expression.” British Journal of Pharmacology, Blackwell Publishing

Ltd, May 2009, www.ncbi.nlm.nih.gov/pmc/articles/PMC2629647/.

Diehl, Paul. “Learn About Genetically Modified Food and How We Got Here.” The Balance, www.thebalance.com/genetically-modified-

food-how-did-we-get-here-375719.

Fire, Andrew Z., and Craig C. Mellow. “Press Release.” Nobelprize.org, 2 Oct. 2006, www.nobelprize.org/nobel_prizes/medicine/

laureates/2006/press.html.

“Genetic Timeline.” National Human Genome Research Institution, NIH, www.genome.gov/pages/education/genetictimeline.pdf.

Harris, Lissa. “The DNA Microarray.” The Scientist, www.the-scientist.com/?articles.view/articleNo/16657/title/The-DNA-

Microarray/.

History.com Staff. “Watson and Crick Discover Chemical Structure of DNA.” History.com, A+E Networks, 2009, www.history.com/this-

day-in-history/watson-and-crick-discover-chemical-structure-of-dna

Norkin, Leonard. “A Most ‘Elegant’ Experiment: Sydney Brenner, Francois Jacob, Mathew Meselson, and the Discovery of Messenger

RNA.” Norkin Virology Site, 12 Oct. 2016, norkinvirology.wordpress.com/2016/10/06/a-most-elegant-experiment-sydney-brenner-frjacob-mathew-meselson-and-the-discovery-of-messenger-rna/.

Oswald, Dr. Nick. “The Invention of PCR.” Bitesize Bio, 24 Oct. 2007, bitesizebio.com/13505/the-invention-of-pcr/.

“Restriction Fragment Length Polymorphism.” Science Direct, www.sciencedirect.com/topics/neuroscience/restriction-fragment-length-

polymorphism.

The Editors of Encyclopædia Britannica. “Walther Flemming.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 28 Oct. 2016,

www.britannica.com/biography/Walther-Flemming.

“The Life of Dolly.” Dolly @20, dolly.roslin.ed.ac.uk/facts/the-life-of-dolly/index.html.

“The Rosalind Franklin Papers.” U.S. National Library of Medicine, National Institutes of Health, profiles.nlm.nih.gov/ps/

retrieve/Narrative/KR/p-nid/187.

Woo, Dr. Joseph. “Amniocentesis.” A Short History of Amniocentesis, Fetoscopy and Chorionic Villus Sampling, www.ob-

ultrasound.net/amniocentesis.html.

Anusha Gopalam &

Katie Greiner

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