Advances in Genetics: 56

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One of the main recommendations from this meeting was that government oversight of recombinant DNA research should be established until the technology was deemed safe. In Genentech , the first genetic engineering company, was founded by Herbert Boyer and Robert Swanson and a year later the company produced a human protein somatostatin in E. Genentech announced the production of genetically engineered human insulin in Supreme Court in the Diamond v. Chakrabarty case ruled that genetically altered life could be patented. The first field trials of genetically engineered plants occurred in France and the USA in , tobacco plants were engineered to be resistant to herbicides.

In , scientists at the J. Craig Venter Institute created the first synthetic genome and inserted it into an empty bacterial cell.

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The resulting bacterium, named Mycoplasma laboratorium , could replicate and produce proteins. Creating a GMO is a multi-step process. Genetic engineers must first choose what gene they wish to insert into the organism. This is driven by what the aim is for the resultant organism and is built on earlier research. Genetic screens can be carried out to determine potential genes and further tests then used to identify the best candidates. The development of microarrays , transcriptomics and genome sequencing has made it much easier to find suitable genes.

The next step is to isolate the candidate gene. The cell containing the gene is opened and the DNA is purified. If the chosen gene or the donor organism's genome has been well studied it may already be accessible from a genetic library. If the DNA sequence is known, but no copies of the gene are available, it can also be artificially synthesised. The plasmid is replicated when the bacteria divide, ensuring unlimited copies of the gene are available. Before the gene is inserted into the target organism it must be combined with other genetic elements.

These include a promoter and terminator region, which initiate and end transcription. A selectable marker gene is added, which in most cases confers antibiotic resistance , so researchers can easily determine which cells have been successfully transformed. The gene can also be modified at this stage for better expression or effectiveness. These manipulations are carried out using recombinant DNA techniques, such as restriction digests , ligations and molecular cloning. There are a number of techniques available for inserting the gene into the host genome. Some bacteria can naturally take up foreign DNA.

This ability can be induced in other bacteria via stress e. DNA is generally inserted into animal cells using microinjection , where it can be injected through the cell's nuclear envelope directly into the nucleus , or through the use of viral vectors. In plants the DNA is often inserted using Agrobacterium -mediated recombination , [59] taking advantage of the Agrobacterium s T-DNA sequence that allows natural insertion of genetic material into plant cells.

Due to the damage caused to the cells and DNA the transformation efficiency of biolistics and electroporation is lower than agrobacterial transformation and microinjection. As only a single cell is transformed with genetic material, the organism must be regenerated from that single cell. In plants this is accomplished through the use of tissue c ulture. Selectable markers are used to easily differentiate transformed from untransformed cells. These markers are usually present in the transgenic organism, although a number of strategies have been developed that can remove the selectable marker from the mature transgenic plant.

The presence of the gene does not guarantee it will be expressed at appropriate levels in the target tissue so methods that look for and measure the gene products RNA and protein are also used. The new genetic material can be inserted randomly within the host genome or targeted to a specific location. The technique of gene targeting uses homologous recombination to make desired changes to a specific endogenous gene.

This tends to occur at a relatively low frequency in plants and animals and generally requires the use of selectable markers. The frequency of gene targeting can be greatly enhanced through genome editing. There are four families of engineered nucleases: Genetic engineering has applications in medicine, research, industry and agriculture and can be used on a wide range of plants, animals and micro organisms.

Bacteria , the first organisms to be genetically modified, can have plasmid DNA inserted containing new genes that code for medicines or enzymes that process food and other substrates.

The genetically modified animals include animals with genes knocked out , increased susceptibility to disease , hormones for extra growth and the ability to express proteins in their milk. Genetic engineering has many applications to medicine that include the manufacturing of drugs, creation of model animals that mimic human conditions and gene therapy. One of the earliest uses of genetic engineering was to mass-produce human insulin in bacteria.

FDA as a treatment for the cancer acute lymphoblastic leukemia. Genetically engineered viruses are being developed that can still confer immunity, but lack the infectious sequences. Genetic engineering is also used to create animal models of human diseases. Genetically modified mice are the most common genetically engineered animal model. Also genetically modified pigs have been bred with the aim of increasing the success of pig to human organ transplantation. Gene therapy is the genetic engineering of humans , generally by replacing defective genes with effective ones.

Clinical research using somatic gene therapy has been conducted with several diseases, including X-linked SCID , [92] chronic lymphocytic leukemia CLL , [93] [94] and Parkinson's disease.

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Researchers are altering the genome of pigs to induce the growth of human organs to be used in transplants. Scientists are creating "gene drives", changing the genomes of mosquitoes to make them immune to malaria, and then spreading the genetically altered mosquitoes throughout the mosquito population in the hopes of eliminating the disease. Genetic engineering is an important tool for natural scientists. Genes and other genetic information from a wide range of organisms can be inserted into bacteria for storage and modification, creating genetically modified bacteria in the process. Once a gene is isolated it can be stored inside the bacteria providing an unlimited supply for research.

Organisms are genetically engineered to discover the functions of certain genes. This could be the effect on the phenotype of the organism, where the gene is expressed or what other genes it interacts with. These experiments generally involve loss of function, gain of function, tracking and expression. Organisms can have their cells transformed with a gene coding for a useful protein, such as an enzyme, so that they will overexpress the desired protein. Mass quantities of the protein can then be manufactured by growing the transformed organism in bioreactor equipment using industrial fermentation , and then purifying the protein.

In materials science , a genetically modified virus has been used in a research laboratory as a scaffold for assembling a more environmentally friendly lithium-ion battery. One of the best-known and controversial applications of genetic engineering is the creation and use of genetically modified crops or genetically modified livestock to produce genetically modified food. Crops have been developed to increase production, increase tolerance to abiotic stresses , alter the composition of the food, or to produce novel products. The first crops to be realised commercially on a large scale provided protection from insect pests or tolerance to herbicides.

Fungal and virus resistant crops have also been developed or are in development. GMOs have been developed that modify the quality of produce by increasing the nutritional value or providing more industrially useful qualities or quantities. Soybeans and canola have been genetically modified to produce more healthy oils. Plants and animals have been engineered to produce materials they do not normally make. Pharming uses crops and animals as bioreactors to produce vaccines, drug intermediates, or the drugs themselves; the useful product is purified from the harvest and then used in the standard pharmaceutical production process.

Genetic engineering has potential applications in conservation and natural area management. Gene transfer through viral vectors has been proposed as a means of controlling invasive species as well as vaccinating threatened fauna from disease. Genetic engineering is also being used to create microbial art. The regulation of genetic engineering concerns the approaches taken by governments to assess and manage the risks associated with the development and release of GMOs.

The development of a regulatory framework began in , at Asilomar , California. The legal and regulatory status of GM foods varies by country, with some nations banning or restricting them, and others permitting them with widely differing degrees of regulation. Most countries that do not allow GMO cultivation do permit research.

The US policy focuses on the product not the process , only looks at verifiable scientific risks and uses the concept of substantial equivalence. The criteria for authorisation fall in four broad categories: One of the key issues concerning regulators is whether GM products should be labeled.

The European Commission says that mandatory labeling and traceability are needed to allow for informed choice, avoid potential false advertising [] and facilitate the withdrawal of products if adverse effects on health or the environment are discovered. Labeling of GMO products in the marketplace is required in 64 countries. In Canada and the USA labeling of GM food is voluntary, [] while in Europe all food including processed food or feed which contains greater than 0.

Critics have objected to the use of genetic engineering on several grounds, that include ethical, ecological and economic concerns. Many of these concerns involve GM crops and whether food produced from them is safe and what impact growing them will have on the environment. These controversies have led to litigation, international trade disputes, and protests, and to restrictive regulation of commercial products in some countries. Accusations that scientists are " playing God " and other religious issues have been ascribed to the technology from the beginning.

Gene flow between GM crops and compatible plants, along with increased use of selective herbicides , can increase the risk of " superweeds " developing. There are three main concerns over the safety of genetically modified food: Such debate, even if positive and part of the natural process of review by the scientific community, has frequently been distorted by the media and often used politically and inappropriately in anti-GE crops campaigns.

Critical Reviews in Biotechnology: Here, we show that a number of articles some of which have strongly and negatively influenced the public opinion on GM crops and even provoked political actions, such as GMO embargo, share common flaws in the statistical evaluation of the data. Having accounted for these flaws, we conclude that the data presented in these articles does not provide any substantial evidence of GMO harm. The presented articles suggesting possible harm of GMOs received high public attention. However, despite their claims, they actually weaken the evidence for the harm and lack of substantial equivalency of studied GMOs.

We emphasize that with over published articles on GMOs over the last 10 years it is expected that some of them should have reported undesired differences between GMOs and conventional crops even if no such differences exist in reality. Journal of the Science of Food and Agriculture. It is therefore not surprising that efforts to require labeling and to ban GMOs have been a growing political issue in the USA citing Domingo and Bordonaba, Overall, a broad scientific consensus holds that currently marketed GM food poses no greater risk than conventional food Major national and international science and medical associations have stated that no adverse human health effects related to GMO food have been reported or substantiated in peer-reviewed literature to date.

Despite various concerns, today, the American Association for the Advancement of Science, the World Health Organization, and many independent international science organizations agree that GMOs are just as safe as other foods. Compared with conventional breeding techniques, genetic engineering is far more precise and, in most cases, less likely to create an unexpected outcome. GM foods currently available on the international market have passed safety assessments and are not likely to present risks for human health. In addition, no effects on human health have been shown as a result of the consumption of such foods by the general population in the countries where they have been approved.

Continuous application of safety assessments based on the Codex Alimentarius principles and, where appropriate, adequate post market monitoring, should form the basis for ensuring the safety of GM foods. Retrieved 21 March In our view, the potential for GM foods to cause harmful health effects is very small and many of the concerns expressed apply with equal vigour to conventionally derived foods.

However, safety concerns cannot, as yet, be dismissed completely on the basis of information currently available. When seeking to optimise the balance between benefits and risks, it is prudent to err on the side of caution and, above all, learn from accumulating knowledge and experience.

Any new technology such as genetic modification must be examined for possible benefits and risks to human health and the environment.

As with all novel foods, safety assessments in relation to GM foods must be made on a case-by-case basis. Members of the GM jury project were briefed on various aspects of genetic modification by a diverse group of acknowledged experts in the relevant subjects. The GM jury reached the conclusion that the sale of GM foods currently available should be halted and the moratorium on commercial growth of GM crops should be continued. These conclusions were based on the precautionary principle and lack of evidence of any benefit.

The Jury expressed concern over the impact of GM crops on farming, the environment, food safety and other potential health effects. The Royal Society review concluded that the risks to human health associated with the use of specific viral DNA sequences in GM plants are negligible, and while calling for caution in the introduction of potential allergens into food crops, stressed the absence of evidence that commercially available GM foods cause clinical allergic manifestations.

The BMA shares the view that that there is no robust evidence to prove that GM foods are unsafe but we endorse the call for further research and surveillance to provide convincing evidence of safety and benefit. From Wikipedia, the free encyclopedia. This is the latest accepted revision , reviewed on 8 September For a non-technical introduction to the topic of genetics, see Introduction to genetics.

Process of inserting new genetic information into existing cells in order to modify a specific organism for the purpose of changing its characteristics. History of genetic engineering. Genetically modified crops and Genetically modified food. Regulation of genetic engineering. Genetically modified food controversies. Environmental Protection Agency online. Retrieved 16 July Pure and Applied Chemistry. Ethical Issues in Scientific Research: Official Journal of the European Communities. The manipulation of an organism's genetic endowment by introducing or eliminating specific genes through modern molecular biology techniques.

A broad definition of genetic engineering also includes selective breeding and other means of artificial selection. Archived from the original PDF on 11 May Archived from the original PDF on 7 July United States Department of Agriculture, "Genetic modification: The production of heritable improvements in plants or animals for specific uses, via either genetic engineering or other more traditional methods.

Some countries other than the United States use this term to refer specifically to genetic engineering. A 'GMO' is a genetically modified organism. Domestication of Plants in the Old World: The origin and spread of plants in the old world. Historical dictionary of science fiction literature.

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Encyclopedia of Science Fiction. Modern Concepts in Nanotechnology, Volume 5. Retrieved 17 July Altered Bacterium Does Its Job: New letters for life's alphabet". The New York Times. Current Technologies in Plant Molecular Breeding: Science in the News. An Introduction to Genetic Engineering. Putting synthesis into biology". Systems Biology and Medicine.

National Academies Press US. The Biology behind the "Gene-Jockeying" Tool". Microbiology and Molecular Biology Reviews. Assessing Safety and Managing Risk. Plant Cell and Tissue Culture. Current Opinion in Biotechnology. Revolutionizing Detection and Expression Analysis of Genes". Oxford University Press US. Retrieved 15 April Cloned and Genetically Modified Animals". Center for Genetics and Society. Nation Human Genome Research Institute. A double-blind, sham-surgery controlled, randomised trial". Glybera approved by European Commission.

Retrieved on 15 December Retrieved 16 November Archived from the original on 5 August Human germline genetic modification: Retrieved 24 April Retrieved 3 December National Human Genome Research Institute. Unit 13 Genetically Modified Organisms". Protein Engineering and Design. Techniques in Genetic Engineering. Archived from the original on 14 July Retrieved 9 July What are transgenic organisms? In this theory, Ohta stressed the importance of natural selection and the environment to the rate at which genetic evolution occurs.

This technology allows scientists to read the nucleotide sequence of a DNA molecule. At its most fundamental level, inheritance in organisms occurs by passing discrete heritable units, called genes , from parents to offspring. These different, discrete versions of the same gene are called alleles. In the case of the pea, which is a diploid species, each individual plant has two copies of each gene, one copy inherited from each parent. Diploid organisms with two copies of the same allele of a given gene are called homozygous at that gene locus , while organisms with two different alleles of a given gene are called heterozygous.

The set of alleles for a given organism is called its genotype , while the observable traits of the organism are called its phenotype. When organisms are heterozygous at a gene, often one allele is called dominant as its qualities dominate the phenotype of the organism, while the other allele is called recessive as its qualities recede and are not observed. Some alleles do not have complete dominance and instead have incomplete dominance by expressing an intermediate phenotype, or codominance by expressing both alleles at once.

When a pair of organisms reproduce sexually , their offspring randomly inherit one of the two alleles from each parent. These observations of discrete inheritance and the segregation of alleles are collectively known as Mendel's first law or the Law of Segregation. Geneticists use diagrams and symbols to describe inheritance. A gene is represented by one or a few letters. In fertilization and breeding experiments and especially when discussing Mendel's laws the parents are referred to as the "P" generation and the offspring as the "F1" first filial generation.

When the F1 offspring mate with each other, the offspring are called the "F2" second filial generation. One of the common diagrams used to predict the result of cross-breeding is the Punnett square. When studying human genetic diseases, geneticists often use pedigree charts to represent the inheritance of traits. Organisms have thousands of genes, and in sexually reproducing organisms these genes generally assort independently of each other.

This means that the inheritance of an allele for yellow or green pea color is unrelated to the inheritance of alleles for white or purple flowers. This phenomenon, known as " Mendel's second law " or the "law of independent assortment," means that the alleles of different genes get shuffled between parents to form offspring with many different combinations. Some genes do not assort independently, demonstrating genetic linkage , a topic discussed later in this article. Often different genes can interact in a way that influences the same trait. In the Blue-eyed Mary Omphalodes verna , for example, there exists a gene with alleles that determine the color of flowers: Another gene, however, controls whether the flowers have color at all or are white.

When a plant has two copies of this white allele, its flowers are white—regardless of whether the first gene has blue or magenta alleles. This interaction between genes is called epistasis , with the second gene epistatic to the first. Many traits are not discrete features e. These complex traits are products of many genes. The degree to which an organism's genes contribute to a complex trait is called heritability. For example, human height is a trait with complex causes. The molecular basis for genes is deoxyribonucleic acid DNA.

DNA is composed of a chain of nucleotides , of which there are four types: Genetic information exists in the sequence of these nucleotides, and genes exist as stretches of sequence along the DNA chain. DNA normally exists as a double-stranded molecule, coiled into the shape of a double helix. Each nucleotide in DNA preferentially pairs with its partner nucleotide on the opposite strand: A pairs with T, and C pairs with G.

Thus, in its two-stranded form, each strand effectively contains all necessary information, redundant with its partner strand. This structure of DNA is the physical basis for inheritance: DNA replication duplicates the genetic information by splitting the strands and using each strand as a template for synthesis of a new partner strand. Genes are arranged linearly along long chains of DNA base-pair sequences.

In bacteria , each cell usually contains a single circular genophore , while eukaryotic organisms such as plants and animals have their DNA arranged in multiple linear chromosomes. These DNA strands are often extremely long; the largest human chromosome, for example, is about million base pairs in length. While haploid organisms have only one copy of each chromosome, most animals and many plants are diploid , containing two of each chromosome and thus two copies of every gene.

Many species have so-called sex chromosomes that determine the gender of each organism.

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In evolution, this chromosome has lost most of its content and also most of its genes, while the X chromosome is similar to the other chromosomes and contains many genes. The X and Y chromosomes form a strongly heterogeneous pair. When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosis , is the simplest form of reproduction and is the basis for asexual reproduction. Asexual reproduction can also occur in multicellular organisms, producing offspring that inherit their genome from a single parent.

Offspring that are genetically identical to their parents are called clones. Eukaryotic organisms often use sexual reproduction to generate offspring that contain a mixture of genetic material inherited from two different parents. The process of sexual reproduction alternates between forms that contain single copies of the genome haploid and double copies diploid. Diploid organisms form haploids by dividing, without replicating their DNA, to create daughter cells that randomly inherit one of each pair of chromosomes.

Most animals and many plants are diploid for most of their lifespan, with the haploid form reduced to single cell gametes such as sperm or eggs. Some bacteria can undergo conjugation , transferring a small circular piece of DNA to another bacterium. The diploid nature of chromosomes allows for genes on different chromosomes to assort independently or be separated from their homologous pair during sexual reproduction wherein haploid gametes are formed.

In this way new combinations of genes can occur in the offspring of a mating pair. Genes on the same chromosome would theoretically never recombine. However, they do, via the cellular process of chromosomal crossover. During crossover, chromosomes exchange stretches of DNA, effectively shuffling the gene alleles between the chromosomes. The first cytological demonstration of crossing over was performed by Harriet Creighton and Barbara McClintock in Their research and experiments on corn provided cytological evidence for the genetic theory that linked genes on paired chromosomes do in fact exchange places from one homolog to the other.

The probability of chromosomal crossover occurring between two given points on the chromosome is related to the distance between the points. For an arbitrarily long distance, the probability of crossover is high enough that the inheritance of the genes is effectively uncorrelated. The amounts of linkage between a series of genes can be combined to form a linear linkage map that roughly describes the arrangement of the genes along the chromosome. Genes generally express their functional effect through the production of proteins , which are complex molecules responsible for most functions in the cell.

Proteins are made up of one or more polypeptide chains, each of which is composed of a sequence of amino acids , and the DNA sequence of a gene through an RNA intermediate is used to produce a specific amino acid sequence. This process begins with the production of an RNA molecule with a sequence matching the gene's DNA sequence, a process called transcription. This messenger RNA molecule is then used to produce a corresponding amino acid sequence through a process called translation.

Each group of three nucleotides in the sequence, called a codon , corresponds either to one of the twenty possible amino acids in a protein or an instruction to end the amino acid sequence ; this correspondence is called the genetic code. The specific sequence of amino acids results in a unique three-dimensional structure for that protein, and the three-dimensional structures of proteins are related to their functions.

Proteins can bind to other proteins and simple molecules, sometimes acting as enzymes by facilitating chemical reactions within the bound molecules without changing the structure of the protein itself.

Protein structure is dynamic; the protein hemoglobin bends into slightly different forms as it facilitates the capture, transport, and release of oxygen molecules within mammalian blood. A single nucleotide difference within DNA can cause a change in the amino acid sequence of a protein. Because protein structures are the result of their amino acid sequences, some changes can dramatically change the properties of a protein by destabilizing the structure or changing the surface of the protein in a way that changes its interaction with other proteins and molecules.

These sickle-shaped cells no longer flow smoothly through blood vessels , having a tendency to clog or degrade, causing the medical problems associated with this disease. In some cases, these products fold into structures which are involved in critical cell functions e. Although genes contain all the information an organism uses to function, the environment plays an important role in determining the ultimate phenotypes an organism displays. The phrase " nature and nurture " refers to this complementary relationship. The phenotype of an organism depends on the interaction of genes and the environment.

An interesting example is the coat coloration of the Siamese cat. In this case, the body temperature of the cat plays the role of the environment. The cat's genes code for dark hair, thus the hair-producing cells in the cat make cellular proteins resulting in dark hair. But these dark hair-producing proteins are sensitive to temperature i.

In a low-temperature environment, however, the protein's structure is stable and produces dark-hair pigment normally. The protein remains functional in areas of skin that are colder—such as its legs, ears, tail and face—so the cat has dark-hair at its extremities. Environment plays a major role in effects of the human genetic disease phenylketonuria. However, if someone with the phenylketonuria mutation follows a strict diet that avoids this amino acid, they remain normal and healthy. A common method for determining how genes and environment "nature and nurture" contribute to a phenotype involves studying identical and fraternal twins , or other siblings of multiple births.

Fraternal twins are as genetically different from one another as normal siblings.

Genetic engineering

By comparing how often a certain disorder occurs in a pair of identical twins to how often it occurs in a pair of fraternal twins, scientists can determine whether that disorder is caused by genetic or postnatal environmental factors — whether it has "nature" or "nurture" causes. One famous example involved the study of the Genain quadruplets , who were identical quadruplets all diagnosed with schizophrenia. The genome of a given organism contains thousands of genes, but not all these genes need to be active at any given moment. A gene is expressed when it is being transcribed into mRNA and there exist many cellular methods of controlling the expression of genes such that proteins are produced only when needed by the cell.

Transcription factors are regulatory proteins that bind to DNA, either promoting or inhibiting the transcription of a gene. However, when tryptophan is already available to the cell, these genes for tryptophan synthesis are no longer needed. The presence of tryptophan directly affects the activity of the genes—tryptophan molecules bind to the tryptophan repressor a transcription factor , changing the repressor's structure such that the repressor binds to the genes.

The tryptophan repressor blocks the transcription and expression of the genes, thereby creating negative feedback regulation of the tryptophan synthesis process. Differences in gene expression are especially clear within multicellular organisms , where cells all contain the same genome but have very different structures and behaviors due to the expression of different sets of genes. All the cells in a multicellular organism derive from a single cell, differentiating into variant cell types in response to external and intercellular signals and gradually establishing different patterns of gene expression to create different behaviors.

As no single gene is responsible for the development of structures within multicellular organisms, these patterns arise from the complex interactions between many cells. Within eukaryotes , there exist structural features of chromatin that influence the transcription of genes, often in the form of modifications to DNA and chromatin that are stably inherited by daughter cells.

Because of epigenetic features, different cell types grown within the same medium can retain very different properties. Although epigenetic features are generally dynamic over the course of development, some, like the phenomenon of paramutation , have multigenerational inheritance and exist as rare exceptions to the general rule of DNA as the basis for inheritance.

During the process of DNA replication , errors occasionally occur in the polymerization of the second strand. These errors, called mutations , can affect the phenotype of an organism, especially if they occur within the protein coding sequence of a gene. The repair does not, however, always restore the original sequence. In organisms that use chromosomal crossover to exchange DNA and recombine genes, errors in alignment during meiosis can also cause mutations. Mutations alter an organism's genotype and occasionally this causes different phenotypes to appear.

Most mutations have little effect on an organism's phenotype, health, or reproductive fitness. Population genetics studies the distribution of genetic differences within populations and how these distributions change over time. Over many generations, the genomes of organisms can change significantly, resulting in evolution. In the process called adaptation , selection for beneficial mutations can cause a species to evolve into forms better able to survive in their environment.

By comparing the homology between different species' genomes, it is possible to calculate the evolutionary distance between them and when they may have diverged. Genetic comparisons are generally considered a more accurate method of characterizing the relatedness between species than the comparison of phenotypic characteristics.

The evolutionary distances between species can be used to form evolutionary trees ; these trees represent the common descent and divergence of species over time, although they do not show the transfer of genetic material between unrelated species known as horizontal gene transfer and most common in bacteria. Although geneticists originally studied inheritance in a wide range of organisms, researchers began to specialize in studying the genetics of a particular subset of organisms.

The fact that significant research already existed for a given organism would encourage new researchers to choose it for further study, and so eventually a few model organisms became the basis for most genetics research. Organisms were chosen, in part, for convenience—short generation times and easy genetic manipulation made some organisms popular genetics research tools.

Widely used model organisms include the gut bacterium Escherichia coli , the plant Arabidopsis thaliana , baker's yeast Saccharomyces cerevisiae , the nematode Caenorhabditis elegans , the common fruit fly Drosophila melanogaster , and the common house mouse Mus musculus. Medical genetics seeks to understand how genetic variation relates to human health and disease. At the population level, researchers take advantage of Mendelian randomization to look for locations in the genome that are associated with diseases, a method especially useful for multigenic traits not clearly defined by a single gene.

In addition to studying genetic diseases, the increased availability of genotyping methods has led to the field of pharmacogenetics: Individuals differ in their inherited tendency to develop cancer , [89] and cancer is a genetic disease. Mutations occasionally occur within cells in the body as they divide. Although these mutations will not be inherited by any offspring, they can affect the behavior of cells, sometimes causing them to grow and divide more frequently. There are biological mechanisms that attempt to stop this process; signals are given to inappropriately dividing cells that should trigger cell death , but sometimes additional mutations occur that cause cells to ignore these messages.

An internal process of natural selection occurs within the body and eventually mutations accumulate within cells to promote their own growth, creating a cancerous tumor that grows and invades various tissues of the body. Normally, a cell divides only in response to signals called growth factors and stops growing once in contact with surrounding cells and in response to growth-inhibitory signals. It usually then divides a limited number of times and dies, staying within the epithelium where it is unable to migrate to other organs.

To become a cancer cell, a cell has to accumulate mutations in a number of genes three to seven that allow it to bypass this regulation: Although there are some genetic predispositions in a small fraction of cancers, the major fraction is due to a set of new genetic mutations that originally appear and accumulate in one or a small number of cells that will divide to form the tumor and are not transmitted to the progeny somatic mutations.

The most frequent mutations are a loss of function of p53 protein , a tumor suppressor , or in the p53 pathway, and gain of function mutations in the Ras proteins , or in other oncogenes. DNA can be manipulated in the laboratory. Restriction enzymes are commonly used enzymes that cut DNA at specific sequences, producing predictable fragments of DNA. The use of ligation enzymes allows DNA fragments to be connected. By binding "ligating" fragments of DNA together from different sources, researchers can create recombinant DNA , the DNA often associated with genetically modified organisms.

Recombinant DNA is commonly used in the context of plasmids: In the process known as molecular cloning , researchers can amplify the DNA fragments by inserting plasmids into bacteria and then culturing them on plates of agar to isolate clones of bacteria cells — "cloning" can also refer to the various means of creating cloned "clonal" organisms.

DNA sequencing , one of the most fundamental technologies developed to study genetics, allows researchers to determine the sequence of nucleotides in DNA fragments. The technique of chain-termination sequencing , developed in by a team led by Frederick Sanger , is still routinely used to sequence DNA fragments. As sequencing has become less expensive, researchers have sequenced the genomes of many organisms using a process called genome assembly , which utilizes computational tools to stitch together sequences from many different fragments.

Next-generation sequencing or high-throughput sequencing came about due to the ever-increasing demand for low-cost sequencing. These sequencing technologies allow the production of potentially millions of sequences concurrently. Genomics can also be considered a subfield of bioinformatics , which uses computational approaches to analyze large sets of biological data. A common problem to these fields of research is how to manage and share data that deals with human subject and personally identifiable information.

See also genomics data sharing.

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