Molecular genetics
Molecular genetics is the field of biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

 and genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

 that studies the structure and function of gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s at a molecular
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

 level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

 and molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

. It is so-called to differentiate it from other sub fields of genetics such as ecological genetics
Ecological genetics
Ecological genetics is the study of genetics in natural populations.This contrasts with classical genetics, which works mostly on crosses between laboratory strains, and DNA sequence analysis, which studies genes at the molecular level....

 and population genetics
Population genetics
Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...

. An important area within molecular genetics is the use of molecular information to determine the patterns of descent, and therefore the correct scientific classification of organisms
Biological classification
Biological classification, or scientific classification in biology, is a method to group and categorize organisms by biological type, such as genus or species. Biological classification is part of scientific taxonomy....

: this is called molecular systematics.

Along with determining the pattern of descendants, molecular genetics helps in understanding genetic mutations that can cause certain types of diseases. Through utilizing the methods of genetics and molecular biology, molecular genetics discovers the reasons why traits are carried on and how and why some may mutate.

Forward genetics

One of the first tools available to molecular geneticists is the forward genetic screen
Genetic screen
A genetic screen is a procedure or test to identify and select individuals who possess a phenotype of interest. A genetic screen for new genes is often referred to as forward genetics as opposed to reverse genetics, the term for identifying mutant alleles in genes that are already known...

. The aim of this technique is to identify mutations that produce a certain phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

. A mutagen
In genetics, a mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level. As many mutations cause cancer, mutagens are therefore also likely to be carcinogens...

 is very often used to accelerate this process. Once mutants have been isolated, the mutated
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

 gene can be molecularly identified.

Reverse genetics

While forward genetic screens are productive, a more straightforward approach is to simply determine the phenotype that results from mutating a given gene. This is called reverse genetics. In some organisms, such as yeast and mice, it is possible to induce the deletion of a particular gene, creating what's known as a gene "knockout" - the laboratory origin of so-called "knockout mice" for further study. In other words this process involves the creation of transgenic organisms that do not express a gene of interest. Alternative methods of reverse genetic research include the random induction of DNA deletions and subsequent selection for deletions in a gene of interest, as well as the application of RNA interference.

Gene therapy

A mutation in a gene can result in a severe medical condition. A protein encoded by a mutated gene may malfunction and cells that rely on the protein might therefore fail to function properly. This can cause problems for specific tissues or organs, or for the entire body. This might manifest through the course of development
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...

 (like a cleft palate) or as an abnormal response to stimuli (like a peanut allergy
Peanut allergy
Peanut allergy is a type of food allergy distinct from nut allergies. It is a type 1 hypersensitivity reaction to dietary substances from peanuts causing an overreaction of the immune system which in a small percentage of people may lead to severe physical symptoms. It is estimated to affect...

). Conditions related to gene mutations are called genetic disorders. One way to fix such a physiological problem is gene therapy. By adding a corrected copy of the gene, a functional form of the protein can be produced, and affected cells, tissues, and organs may work properly. As opposed to drug-based approaches, gene therapy repairs the underlying genetic defect.

One form of gene therapy is the process of treating or alleviating diseases by genetically modifying the cells of the affected person with a new gene that's functioning properly. When a human disease gene has been recognized molecular genetics tools can be used to explore the process of the gene in both its normal and mutant states. From there, geneticists engineer a new gene that is working correctly. Then the new gene is transferred either in vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...

 or ex vivo
Ex vivo
Ex vivo means that which takes place outside an organism. In science, ex vivo refers to experimentation or measurements done in or on tissue in an artificial environment outside the organism with the minimum alteration of natural conditions...

 and the body begins to make proteins according to the instructions in that gene. Gene therapy has to be repeated several times for the infected patient to continually be relieved, however, as repeated cell division and cell death slowly randomizes the body's ratio of functional-to-mutant genes.

Currently, gene therapy is still being experimented with and products are not approved by the U.S. Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

. There have been several setbacks in the last 15 years that have restricted further developments in gene therapy. As there are unsuccessful attempts, there continue to be a growing number of successful gene therapy transfers which have furthered the research.

Major diseases that can be treated with gene therapy include viral infections, cancers, and inherited disorders, including immune system disorders.

Classical gene therapy

Classical gene therapy is the approach which delivers genes, via a modified virus or "vector"
Vector (molecular biology)
In molecular biology, a vector is a DNA molecule used as a vehicle to transfer foreign genetic material into another cell. The four major types of vectors are plasmids, viruses, cosmids, and artificial chromosomes...

 to the appropriate target cells with a goal of attaining optimal expression of the new, introduced gene. Once inside the patient, the expressed genes are intended to produce a product that the patient lacks, kill diseased cells directly by producing a toxin, or activate the immune system to help the killing of diseased cells.

Nonclassical gene therapy

Nonclassical gene therapy inhibits the expression of genes related to pathogenesis, or corrects a genetic defect and restores normal gene expression.

In vivo gene transfer

During In vivo gene transfer, the genes are transferred directly into the tissue of the patient and this can be the only possible option in patients with tissues where individual cells cannot be cultured in vitro in sufficient numbers (e.g. brain cells). Also, in vivo gene transfer is necessary when cultured cells cannot be re-implanted in patients effectively.

Ex vivo gene transfer

During ex vivo gene transfer the cells are cultured outside the body and then the genes are transferred into the cells grown in culture. The cells that have been transformed successfully are expanded by cell culture and then introduced into the patient.

Principles for gene transfer

Classical gene therapies usually require efficient transfer of cloned genes into the disease cells so that the introduced genes are expressed at sufficiently high levels to change the patient's physiology. There are several different physicochemical and biological methods that can be used to transfer genes into human cells. The size of the DNA fragments that can be transferred is very limited, and often the transferred gene is not a conventional gene. Horizontal gene transfer
Horizontal gene transfer
Horizontal gene transfer , also lateral gene transfer , is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism...

 is the transfer of genetic material from one cell to another that is not its offspring. Artificial horizontal gene transfer is a form of genetic engineering.

Techniques in molecular genetics

There are three general techniques used for molecular genetics: amplification, separation and detection, and expression. Specifically used for amplification is polymerase chain reaction, which is an “indispensable tool in a great variety of applications”. In the separation and detection technique DNA and mRNA are isolated from their cells. Gene expression in cells or organisms is done in a place or time that is not normal for that specific gene.


There are other methods for amplification besides polymerase chain reaction. Cloning DNA in bacteria is also a way to amplify DNA in genes.

Polymerase chain reaction

The main materials used in polymerase chain reaction are DNA nucleotides, template DNA, primers and Taq polymerase. DNA nucleotides are the base for the new DNA, the template DNA is the specific sequence being amplified, primers are complementary nucleotides that can go on either side of the template DNA, and Taq polymerase is a heat stable enzyme that jump-starts the production of new DNA at the high temperatures needed for reaction. This technique does not need to use living bacteria or cells; all that is needed is the base sequence of the DNA and materials listed above.

Cloning DNA in bacteria

The word cloning for this type of amplification entails making multiple identical copies of a sequence of DNA. The target DNA sequence is then inserted into a cloning vector
Cloning vector
A cloning vector is a small piece of DNA into which a foreign DNA fragment can be inserted. The insertion of the fragment into the cloning vector is carried out by treating the vehicle and the foreign DNA with a restriction enzyme that creates the same overhang, then ligating the fragments...

. Because this vector originates from a self-replicating virus, plasmid, or higher organism cell when the appropriate size DNA is inserted the “target and vector DNA fragments are then ligated” and create a recombinant DNA molecule.
The recombinant DNA molecules are then put into a bacteria strain (usually E. coli) which produces several identical copies by transformation. Transformation is the DNA uptake mechanism possessed by bacteria. However, only one recombinant DNA molecule can be cloned within a single bacteria cell, so each clone is of just one DNA insert.

Separation and detection

In separation and detection DNA and mRNA are isolated from cells (the separation) and then detected simply by the isolation. Cell cultures are also grown to provide a constant supply of cells ready for isolation.

Cell cultures

A cell culture
Cell culture
Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...

 for molecular genetics is a culture that is grown in artificial conditions. Some cell types grow well in cultures such a skin cells, but other cells are not as productive in cultures. There are different techniques for each type of cell, some only recently being found to foster growth in stem and nerve cells. Cultures for molecular genetics are frozen in order to preserve all copies of the gene specimen and thawed only when needed. This allows for a steady supply of cells.

DNA isolation

DNA isolation extracts DNA from a cell in a pure form. First, the DNA is separated from cellular components such as proteins, RNA, and lipids. This is done by placing the chosen cells in a tube with a solution that mechanically, chemically, breaks the cells open. This solution contains enzymes, chemicals, and salts that breaks down the cells except for the DNA. It contains enzymes to dissolve proteins, chemicals to destroy all RNA present, and salts to help pull DNA out of the solution.

Next, the DNA is separated from the solution by being spun in a centrifuge, which allows the DNA to collect in the bottom of the tube. After this cycle in the centrifuge the solution is poured off and the DNA is resuspended in a second solution that makes the DNA easy to work with in the future.

This results in a concentrated DNA sample that contains thousands of copies of each gene. For large scale projects such as sequencing
Gene sequencing
Gene Sequencing may refer to:* DNA sequencing* or a comprehensive variant of it: Full genome sequencing...

 the human genome, all this work is done by robots.

mRNA isolation

Expressed DNA that codes for the synthesis of a protein is the final goal for scientists and this expressed DNA is obtained by isolating mRNA (Messenger RNA
Messenger RNA
Messenger RNA is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein...

First, laboratories use a normal cellular modification of mRNA that adds up to 200 adenine
Adenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...

 nucleotides to the end of the molecule (poly(A) tail). Once this has been added, the cell is ruptured and its cell contents are exposed to synthetic beads that are coated with thymine string nucleotides. Because Adenine and Thymine
Thymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be derived by methylation of uracil at...

 pair together in DNA, the poly(A) tail and synthetic beads are attracted to one another, and once they bind in this process the cell components can be washed away without removing the mRNA. Once the mRNA has been isolated, reverse transcriptase
Reverse transcriptase
In the fields of molecular biology and biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase enzyme that transcribes single-stranded RNA into single-stranded DNA. It also helps in the formation of a double helix DNA once the RNA has been reverse...

 is employed to convert it to single-stranded DNA, from which a stable double-stranded DNA is produced using DNA polymerase
DNA polymerase
A DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....

. Complementary DNA
Complementary DNA
In genetics, complementary DNA is DNA synthesized from a messenger RNA template in a reaction catalyzed by the enzyme reverse transcriptase and the enzyme DNA polymerase. cDNA is often used to clone eukaryotic genes in prokaryotes...

 (cDNA) is much more stable than mRNA and so, once the double-stranded DNA has been produced it represents the expressed DNA sequence scientists look for.

The Human Genome Project

The Human Genome Project
Human Genome Project
The Human Genome Project is an international scientific research project with a primary goal of determining the sequence of chemical base pairs which make up DNA, and of identifying and mapping the approximately 20,000–25,000 genes of the human genome from both a physical and functional...

 is a molecular genetics project that began in the 1990s and was projected to take fifteen years to complete. However, because of technological advances the progress of the project was advanced and the project finished in 2003, taking only thirteen years. The project was started by the U.S. Department of Energy and the National Institutes of Health in an effort to reach six set goals. These goals included:
  1. identifying 20,000 to 25,000 genes in human DNA (although initial estimates were approximately 100,000 genes),
  2. determining sequences of chemical based pairs in human DNA,
  3. storing all found information into databases,
  4. improving the tools used for data analysis,
  5. transferring technologies to private sectors, and
  6. addressing the ethical, legal, and social issues (ELSI) that may arise from the projects.

The project was worked on by eighteen different countries including the United States, Japan, France, Germany, and the United Kingdom. The collaborative effort resulted in the discovery of the many benefits of molecular genetics. Discoveries such as molecular medicine, new energy sources and environmental applications, DNA forensics, and livestock breeding, are only a few of the benefits that molecular genetics can provide.

See also

  • Gene mapping
    Gene mapping
    Gene mapping, also called genome mapping, is the creation of a genetic map assigning DNA fragments to chromosomes.When a genome is first investigated, this map is nonexistent. The map improves with the scientific progress and is perfect when the genomic DNA sequencing of the species has been...

  • Genomic imprinting
  • Regulation of gene expression
    Regulation of gene expression
    Gene modulation redirects here. For information on therapeutic regulation of gene expression, see therapeutic gene modulation.Regulation of gene expression includes the processes that cells and viruses use to regulate the way that the information in genes is turned into gene products...

  • Differential Susceptibility
    Differential susceptibility hypothesis
    According to the differential susceptibility hypothesis by Belsky individuals vary in the degree they are affected by experiences or qualities of the environment they are exposed to...

Further reading

  • Atlas
    An atlas is a collection of maps; it is typically a map of Earth or a region of Earth, but there are atlases of the other planets in the Solar System. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats...

     of Genetics
    Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

     and Cytogenetics
    Cytogenetics is a branch of genetics that is concerned with the study of the structure and function of the cell, especially the chromosomes. It includes routine analysis of G-Banded chromosomes, other cytogenetic banding techniques, as well as molecular cytogenetics such as fluorescent in situ...

     in Oncology
    Oncology is a branch of medicine that deals with cancer...

     and Haematology
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