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 Table of Contents  
CURRICULUM IN CARDIOLOGY - HISTORY OF MEDICINE
Year : 2018  |  Volume : 4  |  Issue : 3  |  Page : 224-232

Story of gene: Part II – Genetics and genomics


1 Division of Forensic Science, School of Basic and Applied Sciences, Galgotias University, Greater Noida, Uttar Pradesh, India
2 Department of Cardiology, AIIMS, New Delhi, India
3 Division of Forensic Chemistry and Toxicology, College of Natural Sciences, Arba Minch University, Arba Minch, Ethiopia

Date of Web Publication11-Jan-2019

Correspondence Address:
Dr. Amitabh Biswas
College of Natural Sciences, Arba Minch University, Arba Minch
Ethiopia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jpcs.jpcs_63_18

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  Abstract 

Living beings are encoded with the genes as a hereditary material and genetics deal with the functional and structural study of these genes. Since its discovery by Mendel, still we are struggling to completely elucidate the world, the gene, and its interactions. From pea plant experiments to human genome, numbers of eminent scientists had given their contributions in understanding the vast galaxy of genetic nodes in the genome. With the DNA technology advancement, in the near future, we may able to understand molecular mechanisms of human body leading to customized medicines termed as personalized medicine. In this article, we had taken further the story of gene part I to extend our acquaintance before human genetics. We had also given special context to Indian scientist making remarkable achievement in the field of genetics and genomics.

Keywords: Clustered regularly interspaced short palindromic repeats-Cas, epigenetics, next-generation sequencing, personalized medicine


How to cite this article:
Sharma P, Das S, Biswas A. Story of gene: Part II – Genetics and genomics. J Pract Cardiovasc Sci 2018;4:224-32

How to cite this URL:
Sharma P, Das S, Biswas A. Story of gene: Part II – Genetics and genomics. J Pract Cardiovasc Sci [serial online] 2018 [cited 2019 Aug 23];4:224-32. Available from: http://www.j-pcs.org/text.asp?2018/4/3/224/249944


  Introduction Top


After the discovery of DNA in the cell was confirmed, many scientists found clues for the discoveries and inventions that brought an evolution in the genomics era. After the greatest discovery of Rosalind Franklin and later James Watson and Francis Crick who were successful in explaining the double-helical structure of DNA, many other scientists worked on DNA to reveal the existence of life and to bring the advancements in the DNA technologies. These advancements and technologies lead to modern genetics, which agree with the Mendel concept but with certain modifications. In this article, we will try to enlist eminent scientists who had contributed essentially to genetics.

Alexander Robertus Todd (October 2, 1907–January 10, 1997)

After, Watson and Crick, the conformational structure of DNA, on the other hand, a British Biochemist, Alexander Robertus Todd stated the chemical built-up of nucleotides. He was born in a business class family in Glasgow, Scotland. He finished his thesis on the chemistry of apocholic acid, one of the bile acids, for which he received his Ph.D. from the University of Frankfurt am Main in 1931. He was also assigned as the Director of the Chemistry Laboratory at the University of Manchester from 1938 to 1944, where he started his work on nucleotides, structural units of nucleic acids, that is, DNA and RNA. He stated the chemical makeup of the nucleotides. Furthermore, he synthesized all the major nucleotides and nucleosides: adenosine triphosphate, flavin-adenine dinucleotide, nicotinamide adenine dinucleotide, and uridine-diphosphate glucose. He used various chemical methods and also developed some methods for the synthesis of oligonucleotides for which he was awarded with the Nobel Prize for Chemistry in 1957 for this work [Figure 1].[1],[2]
Figure 1: Structure of adenosine triphosphate (source: Available from: http://www.loretocollegebiology.weebly.com/atp-structure--function.html. [Last accessed on 2018 Dec 05]).

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He elucidated the structure of nucleotides. The nucleotides made up of three major components; (1) 5'-sugar (pentose), (2) Phosphate group, and (3) Nitrogenous bases (adenine, thymine, guanine, cytosine, and uracil) along with their structural properties. They were categorized as: purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil).


  The Chromosome Number of Man Top


It was a greatest achievement to decipher the structure and function of the chromosome, a densely packed material that is found in the nucleus of a cell. In 1842, Carl Wilhelm von Naegeli, a Swiss Botanist, was thefirst person who observed some entities while examining a plant cell.[3],[4] Later in 1882, a German Biologist, Walther Flemming also the founder of cytogenetics while examining the cell structure, he observed some thread-like entities which divide during the process of cell division and named it “chromatin.” He also discovered the systematic pattern of cell division which he called mitosis. In the year 1888, after the discovery of thread-like structure, another German Anatomist, Heinrich von Waldeyer, who contributed in coining the term “Chromosome” for those thread-like structures in the nucleus of the cell.[4]

The concept of the inheritance was successfully demonstrated by Gregor J. Mendel in 1865 by his work on Pisum sativum, and following that several researches were carried out to reveal the pattern of inheritance. In the year 1902–1904, two scientists Walter Sutton and Theodor Boveri proposed a theory which got famous as “The Chromosomal Theory of Inheritance.” They both independently worked on the inheritance pattern and the related aspects. Walter Sutton, 1902, in his study on the chromosomes of the grasshopper, Brachystola, found that the chromosomes segregate into the pairs while cell division and carry the factor of inheritance with them to the next generation.[5],[6] Meanwhile, Theodor Boveri, 1904, proposed the same theory while studying the embryology and fertilization in sea urchin, he found a correlation between the Mendelian factors and the division of chromosomes in the cell during meiosis.[3],[4] They both formed the basis of inheritance and explained the relationship between Mendel's Laws and inheritance through the chromosomes.

E.B. Wilson, friends with Theodor Boveri and professor of Walter Sutton, named the chromosomal theory of inheritance as “The Sutton-Boveri Theory.”[6]

In 1912, Hans von Winiwarter, reported the total count of 47 chromosomes in testes and 48 chromosomes in the fetal ovaries. Furthermore, Theophilus S. Painter, 1921, reported the 48 chromosomes in the male testes along with the presence of Y-chromosome.[7],[8]

In 1955, Joe Hin Tjio made an outbreaking discovery which made every existing possibility of number of chromosomes to be failed. He held a position in the laboratory of Albert Levan at University of Lund, Sweden. Tjio and Levan stated that the total number of chromosomes in humans was 46 instead of any 47 or 48. They worked on the lung tissues which were taken from the lungs of embryos that were legally aborted there. In 1956, his work also got published in the Hereditas [Figure 2].[8]
Figure 2: Joe Hin Tjio, man behind giving the 46 as the total number of chromosomes in humans (Adopted from: Hsu TC. Human and Mammalian Cytogenetics: An Historical Perspective. New York: Springer; 1979).

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  The Meselson and Stahl Experiment Top


The genetic code

The genetic code is the coding system that helps in determining the information that is carried by DNA or RNA in the form of codons. The codons occur in the form of triplets and each triplet encodes a specific amino acid. There are total 64 codons in number. There are a vast history and the contribution of several numbers of scientists behind postulating this genetic code system. We will discuss in brief, how we come to know about the genetic code in a chronological way.

In 1957–1958, Robert William Holley, an American Biochemist, and Marshall Warren Nirenberg, a Jewish American Biochemist and Geneticist, both were successful in establishing a link between the messenger RNA nucleotide sequence and the related polypeptide sequence. Robert William Holley aimed at sequencing the entire sequence of tRNA, in which he worked on the sequencing of alanine tRNA. He, based on finding the anticodons of the mRNA nucleotide sequence, presented his work “The nucleotide sequence of a nucleic acid” in the Scientific American.[9]

Later in the year 1961, Sydney Brenner, a South African Biologist; Francois Jacob, a French Biologist; and Matthew Meselson, an American Geneticist and Molecular Biologist, identified the role of messenger RNA. They elucidated that the role of messenger RNA is to transmit the information from the DNA code in protein synthesizing. Sydney Brenner, in addition, along with the help of Francis Crick discovered the frameshift mutation in the same year 1961.[10],[11]

Followed by this in the same year, Marshall Warren Nirenberg, along with the J. Heinrich Matthaei, a German Biochemist at the National Institute of Health (NIH) in Bethesda, Maryland, were thefirst to reveal the nature of codon. They experimentally described the nature of codon by adding a synthetic RNA molecule which comprised of the repeating unit of uridine (poly-U) to the cell-free extract of colon bacillus and ends up resulting in getting a protein-like molecule of repeating unit of phenylalanine, one of the standard amino acids.[11],[12],[13]

George Gamow was a Soviet-American theoretical Physicist and Cosmologist, who made us understood the arrangement of all the four bases of DNA that leads to the protein synthesis. He postulated that the possible permutation of all the four bases comes out to be 64 (i.e., 4 × 4 × 4 = 64). Hence, he stated that there is always a pair of three bases out of 4, which makes a specific codon which encodes a specific amino acid out of the 20 standard amino acids. In addition, he stated that any change in the single base could change the further nucleotide sequence which results in the change of amino acid sequence.[13],[14]

Later in the year 1966, the whole genetic code was cracked. Marshall W. Nirenberg, along with the help of Robert W. Holley and Har Gobind Khorana, was successful in elucidating the whole genetic code system. Finally in 1966, after several years of research, a perfect genetic code system was established. Nirenberg, Holley, and Khorana got Nobel Prize in Physiology or Medicine in 1968 for “The interpretation of the genetic code and its function in protein synthesis.”[15],[16]

Har Gobind Khorana, a Punjabi American Biochemist, was born in Raipur, Punjab (now in Pakistan). He did his PhD. with J. S. Beer at University of Liverpool in 1948. He helped Marshall W. Nirenberg in deciphering the whole genetic code system by adding important information such as a single amino acid is specified by three nucleotides. In addition, he stated that the codons do not overlap each other and also identified the stop codons.[15] Besides playing the role in the genetic code system, he worked on the complete synthesis of a tyrosine suppressor tRNA.[17],[18] Har Gobind Khorana died at the age of 89, on November 9, 2011, and left behind a great contribution in the history of deciphering the genetic code [Figure 3].[15]
Figure 3: (a) Har Gobind Khorana (1922–2011); (b) Marshall Warren Nirenberg (1927–2010) and (c) Robert William Holley (1922–1993) who contributed in deciphering the genetic code (source; a, Ansari, et al. Har Gobind Khorana 1922-2011. Obituary 147:1433-5.; b, Available from: http://www.edubilla.com/award/national-medal-of-science/marshall-warren-nirenberg/. [Last accessed on 2018 Dec 05].; c, Robert W. Holley– biographical. NobelPrize.org. Nobel Media AB; 2018. Available from: https://www.nobelprize.org/prizes/medicine/1968/holley/biographical/. [Last accessed on 2018 Nov 05]).

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  The Era of the DNA Sequencing Top


In the early 1970s, when DNA discovery was making huge impact in genetics, several other inventions took place which changed the perspective to look toward life form. After deciphering the genetic code system, the protein synthesis mechanism was now understandable. In the year 1970, discovery of restriction enzymes took place. Hamilton O. Smith, an American Microbiologist along with Kent W. Wilcox, discovered the enzymes which cut the DNA at specific sites and named them restriction endonucleases. Later, the name of restriction enzyme type II, they discovered was known has HindII.[19] This advancement in the world of DNA was then followed by the development of recombinant DNA technology. Stanley Norman Cohen, an American Geneticist along with the Herbert Boyer, a researcher and an entrepreneur in biotechnology and Paul Berg, an American Biochemist in the year 1973 successfully constructed thefirst recombinant DNA which was published as “Construction of Biologically Functional Bacterial Plasmids in vitro.”[20] The invention of recombinant DNA was major push toward DNA which leads to the birth of Biotech Industry.

Moreover, along with these discoveries, various techniques were developed to bring out the DNA into the coming genomics era. In the 1970s, various methods of labeling the nucleic acid were developed which uses the immunofluorescence techniques of tagging the DNA for its visualization. Using these methods, several researchers found new ways to sequence the DNA. The major contribution in sequencing of DNA was made by the following scientists.

Frederick Sanger

A British Biochemist, also known to be the “Father of Genomics,” was born on August 13, 1918, in Gloucestershire, England. He studied natural science from St. John's College, Cambridge in 1936. He studied his PhD in 1940, in which he worked on the edible proteins obtained from the grass. Later, he determined the composition of the amino acids of insulin in which he described the chain A and B structure of the insulin molecule and demonstrated that the amino acid sequence does not vary. He was awarded with the Nobel Prize in 1958 in Chemistry for his work on Insulin. After few years, thefirst DNA was sequenced in the laboratory of Sanger. In 1977, he sequenced the entire genome of bacteriophage ϕ-X174, and also he sequenced the entire mitochondrial DNA of humans. He developed a method which now popularly known as “chain-termination method of DNA sequencing [Figure 4].”[21],[22]
Figure 4: Frederick Sanger (1918–2013): Two time Nobel Prize winner for his work on sequencing method (source: Available from: http://www.darwins-god.blogspot.com/2013/11/fred-sanger-protein-sequences-and.html. [Last accessed on 2018 Dec 05]).

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In this method, he employed the use of DNA polymerase I to incorporate the ddNTP and dNTP which were incubated with the primer and template strand. The incorporation of dNTP elongated the oligonucleotide chain, but whenever a ddNTP was incorporated the chain terminated due to the absence of 3'-hydroxyl group. This was then visualized by running it on the electrophoretic gel, and band pattern was determined to know the nucleotide pattern.[23]

He later published his work as “DNA Sequencing with Chain-Terminating Inhibitors” in December 1977. He received the second Nobel Prize in Chemistry in 1980 which he half shared with Maxam and Gilbert for sequencing the DNA. In the year 2013, he completed his life journey and died on November 19, 2013, in Cambridge. He was a pioneer to the world of DNA who demonstrated a way to reveal the nature and information that is carried by the genetic material in a technical manner and hence gave rise to the era of genomics.[21],[22],[23]

Walter Gilbert and Allan Maxam

Walter Gilbert, an American Biochemist and molecular biologist, and Allan Maxam, a molecular geneticist, are the other two pioneers who contributed in the sequencing of DNA besides Frederick Sanger. Maxam-Gilbert and Fred Sanger worked independently at different places by different methods on the sequencing of DNA.[24]

Walter Gilbert was born on March 21, 1932, in Boston who later studied graduation at Harvard University and after that he received his PhD. in Physics from the University of Cambridge. Later, he was appointed as the Assistant Professor of Biophysics at Harvard University. Allan Maxam who was born on October 28, 1942, was a student in the laboratory of W. Gilbert at Harvard University. They both together worked on the sequencing of DNA, which is now popularly called as “Maxam–Gilbert Sequencing.”

On the other hand, where Fred Sanger worked on the chain-termination method for sequencing the DNA, Maxam–Gilbert used the “chemical cleavage method of DNA sequencing” in which the one-end of DNA was labeled, which on treating with chemical agents partially cleaved the DNA at four different bases, that is, A, T, G, C., by producing radioactive fragments. It was then visualized on polyacrylamide gel electrophoresis at the point of cleavage. They used four different tubes in which they added different chemical agents for purines and pyrimidines which cleaved DNA at four different sites, that is, (1) guanine/adenine cleavage, (2) adenine-enhanced cleavage, (3) cytosine/thymine cleavage, and (4) cytosine cleavage [Figure 5].[25],[26]
Figure 5: Allan Maxam and Walter Gilbert and their Maxam–Gilbert sequencing method (source Available from: https://www.alchetron.com/Allan-Maxam; https://www.biography.com/people/walter-gilbert-9311111; https://www.en.wikipedia.org/wiki/Maxam–Gilbert_sequencing).

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The Maxam–Gilbert sequencing method got very popular with the Sanger's dideoxy chain-termination method the same year. However, Maxam–Gilbert method was left with a drawback which made Sanger's method to overpower the sequencing world. Maxam–Gilbert method worked on the chemical agents who were radioactive and highly toxic; on the other hand, Sanger did not use any radioactive chemicals which made it a worldwide method of DNA sequencing.

As soon as DNA sequencing methods got spread worldwide, another revolutionary Nobel Prize-winning technique was introduced to the world of genomics. “The polymerase chain reaction” (PCR) was invented in the year 1983 by Kary Banks Mullis. Kary Mullis was an American Biochemist who discovered PCR now became a backbone of almost every biochemistry and molecular biology experiments. For this revolutionary advanced technique of PCR, Kary Mullis was awarded Nobel Prize in the year 1993. PCR is a technique used to amplify or to extend the number of copies of DNA. The basic principle of PCR is the replication of DNA under certain temperature. The major three steps that are involved in a PCR technique as follows: denaturation, annealing, and extension. The basic requirements for the PCR include template, primer, and DNA polymerase (Taq polymerase) under certain temperature with specific number of cycles according to the required number of copies.[27],[28],[29]

With the development of the Sanger's method, Hood et al. added a new improvement in the existing method of DNA sequencing that is the attachment of the fluorescent dyes which could be detected by sensors connected to computer-operated photographic detectors. By using the automated machinery, the DNA could now be sequenced. In 1987, Applied Biosystems, California, first developed the automated DNA sequencer and successfully sequenced two genes. It was totally based on the Sanger's method of DNA sequencing, in which each dNTP on chain termination showed fluorescence and could be detected by the CCD detector, which on detection noted down in the form of four different colored peaks of each dye (FAM, JOE, TAMRA, and ROX) for each specific base nucleotide [Figure 6].[30],[31]
Figure 6: ABI 377 sequencer and fluorescent tagged DNA fragments show different nucleotide reads separated by electrophoresis (nucleotide reads of automated Sanger's sequencing) (courtesy: ABI: www.seqgen.com).

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  DNA Fingerprinting Top


DNA fingerprinting, or DNA profiling or genotyping is a method which is used to establish the identity of a person. Just like a person having a unique pattern of fingerprints, every individual has the unique pattern of DNA which can only be similar to closely related individuals. The technique of DNA fingerprinting was discovered by Sir Alec Jefferys, a British Geneticist. He is crowned with the title of “The Father of DNA Fingerprinting.” He was born on January 09, 1950 in England. In 1977, he completed his PhD and Postdoctorate as well in which he worked on the mitochondria of cultured mammalian cells and the mammalian genes [Figure 7].
Figure 7: Sir Alec Jeffery working in the University of Leicester, 1985 and Dr. Lalji Singh (Father of DNA Fingerprinting in India) (1947–2017) (Source: Available from: https://www.nlm.nih.gov/visibleproofs/galleries/cases/jeffreys.html; http://www.scind.org/1001/History/prof-lalji-singh-father-of-indian-dna-fingerprinting-technology.html. [Last accessed on 2018 Nov 05]).

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In the year 1984, he discovered the DNA fingerprinting using minisatellite in which he demonstrated the variations that occur in the various individual's DNA. He explained that every individual's DNA is 99.9% similar. The only difference of 0.1% makes every individual to establish a unique identity. This difference of 0.1% in DNA comprises of ~3 million base pairs. In early times, the DNA fingerprinting was based on the minisatellites, that is, variable number tandem repeats analysis and the modern times DNA profiling is done with the help of microsatellites, that is, STR analysis (short tandem repeats).[32],[33],[34],[35]

If we talk about India, Dr. Lalji Singh was thefirst person who enlightened the concept of DNA fingerprinting. He is known to be the “Father of DNA Fingerprinting in India.” He was also awarded the Padma Shri in the year 2004. Dr. Lalji Singh was born on July 9, 1947, and later passed away on December 10, 2017, at the age of 70. He was graduated from Banaras Hindu University (BHU) in zoology and cytogenetics in 1964 and completed his masters in 1966. Later, he received his PhD in 1971 in which he worked on “Evolution of Karyotypes in Snakes.”

He was appointed as the Director of CSIR-Centre for Cellular and Molecular Biology from 1998–2009, also he worked as the Vice-chancellor of BHU, India. In 1995, he founded Centre for DNA fingerprinting and diagnostics and in 1998; he founded Laboratory for the Conservation of Endangered Species. He implied all of his knowledge of molecular biology on various aspects of science and technology. His major contribution to Indian Science and Technology was DNA fingerprinting technology. Besides this, he worked in the field of Wildlife Forensics and Wildlife Conservation, The Molecular basis of Sex Determination, DNA bases molecular diagnostics, and Evolution and Migration pattern of Humans. His contribution to Indian scientific world was glorious and especially toward the growth of DNA profiling in India.[36],[37],[38],[39],[40]


  Human Genome Project (1990–2003) Top


The Human Genome Project was officially started in 1990 was successfully completed in 2003 by NIH and US Department of Energy. This project was supported and recommended by the National Research Council. The main objective of this program was to sequence the entire 3 billion bases of the human DNA using Automated Sanger sequencing method as it would be useful in understanding the biology of the human body and had major implications in genome research.

Basically, the Human Genome project was divided into two phases, thefirst phase was shotgun phase and other was finishing phase. In the shotgun phase, appropriate size of DNA fragments was obtained, cloned, and sequenced in overlapping. In the finishing phase, gaps were filled, and sequences of any unknown area were spot on which was not covered in the shotgun phase. The finishing phase yielded 99% output in the final submission. The final form had 2.85 billion nucleotides with error rate 1 in 100,000 bases. The Human Genome Project predicted that two individual had 99.9% identical DNA and human DNA nearly contain 20,000–25,000 genes. Although the Human Genome Project had contributed immensely to our understanding of the molecular mechanisms of several diseases, one of the objectives and hope of curing genetic disorders was not achieved through this project. This suggests that we need to know more than just what the order of sequence is.[41]

After human genome sequencing, now human proteome map project had been started and scientist from Indian origin Akhilesh Pandey, Founder Director of Institute of Bioinformatics along with Harsha Gowda are leading the project. They had targeted 30 different human tissues to identify 17,294 genes encoded protein (84% of total).[42]


  Next-Generation Sequencing Top


After decoding the human genome in 2003, DNA technology rapidly took great interest to sequence whole genome quickly and in cost-effective way. The human sequence obtained by Human Genome Project was proven to be standard for others to advance in the field. From the past few years, Automated Sanger's sequencing has been used for the genome analysis. It is considered to be the “First-Generation Technology,” and the newer and upgraded technology is “Next-Generation Sequencing (NGS).” In this modern sequencing era, the method presently is being used for sequencing the DNA known as “NGS.” Using NGS, an entire human genome can be sequenced massively in parallel very easily and quickly.[43] It is the fastest method of sequencing than any other methods. There are four major technologies based on the chemistry used for the sequencing.[30]

  1. Pyrosequencing (Roche 454)
  2. Reversible terminator sequencing (Illumina)
  3. Sequencing by ligation (SOLiD)
  4. Semiconductor sequencing (Ion Torrent).


The basic steps that are carried to sequence the DNA using NGS are:[44],[45]

  1. Library preparation
  2. Enrichment; if required
  3. Sequencing and Imaging
  4. Data analysis (bioinformatics).


These technologies can be used to sequence entire genome or part of it as per the requirement of the scientific query. Mostly in the clinical sense, the protein-coding regions are more important as any variations in these regions may disturb the protein and ultimately phenotype. Whole exome sequencing (Exome means all the exons, i.e., coding regions) is more applicable as data are easier to handle as compared to the genome and the variations found in these regions can be directly associated with the function of the respective protein. Apart from whole genome and whole exome sequencing, targeted approach can also be adopted where candidate's genes can be selected with respect to question of interest. For example, all the genes which are associated with breast cancer are targeted and also genes which are related to it can be sequenced; it may be 10 to few hundred genes. These NGS platforms had provided a vast amount of data and this need to be analyzed to provide meaningful interpretation. This job of data analysis and interpretation had occupied bioinformaticians to a greater extent. This technology was great help to the Mendelian genetics disorder (Beta thalassemia; Huntington disease, etc.), whereas for the complex diseases (Heart disease; Cancer; Diabetes, etc.), still there is a lot of scope for understanding genome in detail.


  Genetic Engineering Top


The last 60 years of history of genetic material engineering remain very challenging, from that age to modern genetics, tools, and resources available to the genetic engineer had increased to perform extreme challenging targets with scale and precision. Genome engineering deals with the manipulation of genetic material; thefirst technology of this field was invented by Herbert W. Boyer, Stanley N. Cohen, and Paul Berg in the form of recombinant DNA technology in 1972. This technology is the way of introducing genetic material of one organism to other artificially which then replicated and expressed by the other organism. Thefirst genetically modified mouse was developed in 1974 by Rudolf Jaenisch and technology was commercialized within few years which exploded the genetically modified organisms and plants in the market. Insulin is the product of GMO which is the main source of treatment to diabetes. There were many related technologies developed and deletion, insertions, and modifications of genetic materials were done at the genome scale.

To determine the role of a gene, RNAi (RNA Interference) has revolutionized the genome engineering. RNAi provides rapid means in depleting mRNAs by adding double-stranded RNA homologous leading to sequence-specific degradation. It wasfirst reported by Napoli and Jorgensen in 1990 in chalcone synthesis in petunias.[46] RNA silencing wasfirst reported by Guo and Kemphues in animals, they observed that introduction of antisense or sense RNA to mRNA may degrade that mRNA.[47] In the past two decades, the RNAi pathway had become the choice of technology to silence the gene. This exceptional utility of RNAi in modulation gene expression had resulted in deciphering molecular mechanism of genes essential in understanding disease outcome.

Zinc finger nucleases and transcription activator-like effector nucleases (TALENs) were used to create knockout cells. The genetic expressions are controlled by these DNA-binding proteins. Zinc fingers were discovered in 1985 by Miller et al. in Klug laboratory in the protein transcription factor IIIA from Xenopus Oocytes.[48] One of the interesting applications of these zinc fingers peptides to repress the gene expression in mouse cell line. In 1994, Choo and his colleaguesfirst reported such application, this adds to the understanding of zinc fingers in DNA recognition.[49] Another programmable nuclease is TALENs had been widely used for the alteration of DNA sequences. TALENs had been used to modify endogenous genes in yeast, zebra fish, fruit fly, silkworm, rice, human somatic and pluripotent stem cells, and many more.

Currently, clustered regularly interspaced short palindromic repeats (CRISPR) systems had revolutionized the development of genome engineering. CRISPR is an adaptive immune system which was initially discovered in 1987 in the Escherichia coli genome; however, its function was not explained. In 2007, CRISPR was presented as a safeguard against bacteriophage utilizing various CRISPR-Cas protein to store information of invading phages and to response against it on reexposure. In 2012, CRISPR was programmed for targeted DNA cleavage in vitro,[50] and next year, CRISPR-based genome editing mammalian culture was described.[51] Till date, there are more than 7000 publications related to CRISPR and is growing more rapidly. Now, the prime target of this technology is to eradicate genetic disorder through postnatal and germline editing. Despite ethical concern and controversies, CRISPR-Cas genome editing tools are truly remarkable technology for basic research and widely accepted in the research community. Major discoveries in the field of Genetics and Genomics are arranged chronologically in Box along with the discoveries made by Indian scientists.

Future perspective – epigenetics, personalized medicine, and individual responsibility

“This evolution of sequencing the DNA from 1977 till now made a drastic change in the sequencing pattern. Technology brought a revolutionary change from the Sanger's sequencing method to the NGS method, from being sequenced manually to be the automated sequencing. The world of DNA has been evolved.” Regarding future perspective, these technologies are used in studying epigenetics. In recent decades, epigenetics had been focused widely and discovered huge number of molecular mechanism affecting the genes. Epigenetics as the term suggests over the genetics, refers to the outcome of genetic sequence is checked by the epigenetics phenomenon. It had been found that these epigenetics regulations are inherited and can affect future generation or vice-versa. These discoveries are likely to affect the healthcare system in the future, and we need to decide on the personal level. As the genome and epigenome is unique for every individual, so we need to care individually. Therefore, individual responsibility had been increased lately for our lifestyle choices which had more important than ever before.

With all these advancements and individual genetic understanding, the concept of personalized medicine is surfacing in the last few years. Different mutations cause the same phenotype; however, the same mutation may cause different phenotype, with these understandings, tailored medicine could be achieved which will directly benefit the individual.

Acknowledgment

The authors would like to acknowledge the institutions for accessing the online journals through library access.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



Some other Fruitful Discoveries that Happened in the World of DNA

  • 1959-Chromosome abnormalities
  • 1983-Huntington's disease is the first mapped genetic disease
  • 1987-Yoshizumi Ishino, accidentally discovered CRISPR technique
  • 1993-Phillip Allen Sharp and Richard Roberts discovered that the genes of DNA are made up of INTRONS and EXONS and won the Nobel Prize for the same
  • 1994-The First Breast Cancer gene was discovered, BRCA I and BRCA II
  • 1995-Haemophilus influenzae is the first bacterium genome sequenced
  • 1996-Alexander Rich, a scientist who discovered the different conformation of DNA and named it as Z-DNA
  • 1997-Ian Wilmut and colleagues were the first to clone the Dolly Sheep
  • 1999-First Human Chromosome was decoded
  • 2000-The entire genome of Drosophila melanogaster was sequenced
  • 2002-The mouse to be the first mammal whose genome was fully decoded
  • 2003-Human genome was decoded through Sanger sequencing
  • 2010-Transcription activator-like effector nucleases first used to cut specific sequence of DNA
  • 2013-DNA Worldwide and Eurofins Forensic discovered identical twins have difference in genetic makeup
  • 2016-First time genome was sequenced in Outer Space along with the collaboration NASA.


Achievement in Genetics in India

  • 1968-Har Gobind Khorana got Nobel Prize in Physiology or Medicine with two others for “The interpretation of genetic code and its function in protein synthesis”
  • 1984-Obaid Siddiqi was awarded with Padma Bhushan for his work on genetics and neurobiology of Drosophila. He was also known as “Father of Indian Molecular Biology” and Founder of TIFR, Bengaluru
  • 2004-Lalji Singh was awarded the Padma Shri for his contribution in DNA fingerprinting. He is also known as “Father of DNA Fingerprinting in India”
  • 2010– India sequenced its first genome.


 
  References Top

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