Biotechnology Terms Starting With G
Biotechnology Glossary: G
Gel Electrophoresis
/ jel eh-lek-troh-for-EE-sis / · Greek elektron; phoresis, being carried
Gel electrophoresis is a technique that separates nucleic acids or proteins by size and charge as they migrate through a porous gel matrix under the influence of an electric field.
DNA and RNA carry a uniform negative charge and migrate toward the positive electrode, with smaller fragments traveling faster and farther through the gel matrix. Proteins are typically denatured with sodium dodecyl sulfate to impose a uniform negative charge, so polyacrylamide gels separate them by molecular weight rather than native charge. Agarose gels resolve DNA fragments ranging from roughly 100 base pairs to more than 20,000 base pairs, while polyacrylamide gels resolve proteins from approximately 10 to 300 kilodaltons.
The technique is used to verify PCR products, analyze restriction digests, assess RNA integrity, and resolve protein samples before Western blotting.
Kary Mullis, who invented PCR in 1983, relied on agarose gel electrophoresis to confirm that his new amplification method was producing the correct DNA fragment, making gel electrophoresis the first analytical tool used to validate what became one of the most widely used techniques in molecular biology.
Building Blocks of Nucleic Acids →A gel identifies DNA fragments on its own. Gel electrophoresis separates fragments by size, but a size ladder, fluorescent stain such as ethidium bromide or SYBR Safe, or a labeled probe is required to interpret which band corresponds to which fragment.
After amplifying a segment of the BRCA1 gene by PCR, researchers load the product onto a 1.5 percent agarose gel alongside a 100-base-pair DNA ladder. A band appearing at the expected position of 320 base pairs confirms that the correct region was amplified before the sample proceeds to sequencing.
Gene Gun
/ jeen GUN / · Greek genea; Old Norse gunnr
Gene Gun is a device that propels DNA-coated metal microparticles at high velocity into target cells or tissues, enabling the physical introduction of foreign genes without biological vectors.
Gold or tungsten particles 0.4 to 1.2 micrometers in diameter are coated with plasmid DNA and accelerated by helium pressure or a high-voltage electrical discharge into the target tissue. This method delivers DNA to skin, leaf tissue, animal embryos, or organelles such as chloroplasts without requiring competent cell preparation or biological infection. Gene gun delivery to chloroplasts has produced transplastomic tobacco plants expressing foreign proteins at levels exceeding 70 percent of total soluble leaf protein, far above what nuclear transformation typically achieves.
Skin-targeted delivery has also been applied in DNA vaccine development, where resident antigen-presenting cells take up and express the antigen-encoding plasmid.
John Sanford and colleagues at Cornell University invented the gene gun in 1987, originally to transform maize cells that resisted Agrobacterium-mediated transformation. The device was initially nicknamed the "biolistic" gun, a portmanteau of biological and ballistic that remains in common use today.
Cell Wall Functions and Types →A gene gun shoots whole genes like visible bullets. The device fires microscopic metal particles, typically 0.4 to 1.2 micrometers in diameter, that are coated with DNA and invisible to the naked eye.
Researchers used a gene gun to deliver plasmid DNA into immature maize (Zea mays) embryos, producing the first stably transformed maize plants in 1988. Particle bombardment remains a standard transformation method for maize because the species is largely recalcitrant to Agrobacterium infection.
Gene Knockdown
/ jeen NOK-down / · Greek genea; Old Norse knocka
Gene knockdown is the partial reduction of gene expression using RNA interference, antisense oligonucleotides, or other post-transcriptional methods, without permanently altering the genomic DNA sequence.
RNA interference-mediated knockdown uses short double-stranded RNA molecules, either siRNAs delivered exogenously or shRNAs expressed from a vector, that direct the RISC complex to degrade complementary mRNA sequences. Unlike gene knockout, knockdown reduces rather than eliminates expression and is reversible once the silencing molecule is cleared from the cell. A typical siRNA experiment in cultured mammalian cells reduces target mRNA levels by 70 to 95 percent within 48 to 72 hours of transfection.
Knockdown is widely used to study gene function, validate drug targets, and therapeutically silence disease-causing transcripts, as in the FDA-approved siRNA drug inclisiran, which silences PCSK9 mRNA to lower LDL cholesterol.
Andrew Fire and Craig Mello discovered RNA interference in the nematode Caenorhabditis elegans in 1998, showing that injecting double-stranded RNA silenced genes far more potently than single-stranded antisense RNA alone. Their finding earned the Nobel Prize in Physiology or Medicine in 2006 and launched an entirely new class of gene-silencing therapeutics.
Gene knockdown and gene knockout describe the same outcome. Knockdown reduces the amount of mRNA or protein produced while leaving the DNA sequence intact, whereas knockout permanently disrupts the gene sequence so that no functional product is made.
Researchers used siRNA to knock down the expression of the huntingtin gene in cultured striatal neurons derived from mouse models of Huntington's disease. Transfection with 10 nanomolar siRNA reduced mutant huntingtin protein levels by approximately 85 percent within 72 hours, measurably reducing the formation of toxic protein aggregates.
Gene Knockout
/ jeen NOK-out / · Greek genea; Old Norse knocka
Gene knockout is the complete inactivation of a specific gene in a cell or organism, used to determine the gene's function by observing the resulting phenotypic consequences.
Knockouts are created by homologous recombination, CRISPR-mediated frameshift indels, or transposon insertion into the coding sequence. Conditional knockouts using Cre-lox or other site-specific recombinase systems allow gene deletion in specific tissues or at defined developmental stages, avoiding lethality from disrupting genes required for embryonic development. Mario Capecchi, Martin Evans, and Oliver Smithies shared the 2007 Nobel Prize in Physiology or Medicine for developing mouse knockout technology through homologous recombination, a method that took roughly a decade to move from concept to routine laboratory practice.
Genome-wide CRISPR knockout libraries have since enabled systematic screens that identify genes required for specific cellular processes across entire genomes in a single experiment.
The first knockout mouse, generated in 1989 by Martin Evans and colleagues at the University of Cambridge, lacked a functional HPRT gene and served as a model for Lesch-Nyhan syndrome. That single animal demonstrated that targeted gene disruption in mammals was experimentally feasible, opening the door to thousands of subsequent disease models.
Knocking out one gene always kills an organism. Many single-gene knockouts produce no visible phenotype under standard laboratory conditions, because duplicate genes or compensatory pathways maintain normal function; lethality depends entirely on the specific gene and organism involved.
Scientists knocked out the Trp53 gene, which encodes the p53 tumor suppressor, in laboratory mice (Mus musculus). Homozygous knockout mice developed spontaneous tumors, most commonly lymphomas, by 6 months of age, compared with a median tumor-free survival exceeding 24 months in wild-type littermates.
Genetic Engineering
/ jeh-NET-ik en-jih-NEER-ing / · Greek genetikos, of birth; engineer
Genetic engineering is the direct manipulation of an organism's DNA to introduce, remove, or alter specific genes using molecular biology tools.
The field began in 1973 when Herbert Boyer and Stanley Cohen demonstrated that DNA from different organisms could be cut with restriction enzymes and ligated together to form functional recombinant molecules in Escherichia coli. Since then, genetic engineering has produced human insulin expressed in bacteria, recombinant hepatitis B vaccines grown in yeast, herbicide-resistant crops planted on more than 190 million hectares worldwide, and gene therapies that correct inherited disorders in patients. CRISPR-Cas9, first adapted for mammalian genome editing by Feng Zhang and Jennifer Doudna’s groups in 2013, has made precise genome editing accessible to any laboratory with basic molecular biology capability, compressing what once took years of homologous recombination work into a matter of weeks.
Before recombinant DNA technology, insulin for treating diabetes was extracted from the pancreases of slaughtered pigs and cattle, requiring roughly 8,000 pounds of animal tissue to produce one pound of purified insulin. Genentech's bacterially produced human insulin, approved by the FDA in 1982 under the name Humulin, replaced that supply chain within a decade.
Genetic Engineering Pros and Cons →Genetic engineering and selective breeding achieve the same result by the same mechanism. Selective breeding chooses among existing genetic combinations that arise through natural reproduction, whereas genetic engineering directly edits or transfers specific DNA sequences in ways that do not occur through mating.
Engineered Escherichia coli carrying a synthetic human insulin gene on a plasmid produce proinsulin that is then chemically processed into active insulin. A single 10,000-liter fermentation run can yield enough purified insulin to supply thousands of patients for a month.
Genetically Modified Organism
/ jeh-NET-ik-lee MOD-ih-fyd OR-gan-iz-um / · Greek genetikos; Latin modificare; Greek organon + ismos
Genetically Modified Organism is any organism whose genetic material has been altered using genetic engineering techniques to introduce traits not naturally present in that species.
GMOs are created by introducing foreign genes, editing existing genes, or deleting specific sequences to confer traits such as pest resistance, drought tolerance, improved nutritional content, or pharmaceutical production. The first commercialized GMO was the Flavr Savr tomato, approved in 1994, and today over 90% of corn, soybean, and cotton grown in the United States are GMO varieties. Regulatory frameworks for GMO approval vary widely between countries, creating ongoing scientific, ethical, and trade debates.
Some GMOs, such as Golden Rice, are engineered to address nutritional deficiencies rather than agronomic convenience, illustrating the breadth of goals driving the technology.
The bacterium Agrobacterium tumefaciens (now reclassified as Rhizobium radiobacter) has been used for decades to deliver foreign genes into plant cells, and scientists modeled early plant GMO techniques directly on its natural ability to insert DNA into host genomes. This biological mechanism was first characterized in the 1970s and remains one of the most efficient plant transformation tools available.
Genetic Engineering Pros and Cons →All GMOs contain genes from unrelated species. Some are changed by editing their own genes without adding foreign DNA, as with CRISPR-edited crops that carry no transgene at all.
Disadvantages of Genetically Modified Foods →Bt corn (Zea mays) carries a gene from the soil bacterium Bacillus thuringiensis that encodes a protein toxic to certain lepidopteran larvae, including the European corn borer. Fields planted with Bt corn have shown reductions in insecticide applications of up to 90% in some regions, and the trait has been commercially deployed across more than 80 million hectares worldwide.
Genome Assembly
/ JEE-nohm ah-SEM-blee / · Greek genea, birth; nomos, law; Old French assembler
Genome assembly is the computational process of joining millions of short DNA sequence reads, produced by a sequencing instrument, into the complete, ordered sequence of an organism's genome.
A sequencing instrument cannot read an entire chromosome in one pass, so it fragments the DNA into millions of overlapping pieces and reads each one separately, typically generating reads between 150 and 300 base pairs for short-read platforms. Assembly software identifies overlapping sequences and merges them into longer contiguous stretches called contigs, which are then ordered into scaffolds using paired-end or long-read data. Regions with highly repetitive sequences, such as centromeres and telomeres, resist accurate assembly because reads from different copies of a repeat are indistinguishable.
The first complete human genome assembly, published in 2022 by the Telomere-to-Telomere Consortium, required long-read sequencing technology to finally resolve these previously intractable regions.
The 2022 Telomere-to-Telomere human genome assembly filled in roughly 200 million base pairs of sequence that had been missing or misrepresented in the original Human Genome Project reference, including the entire sequence of human centromeres for the first time.
Sequencing a genome automatically delivers a finished, readable sequence. Assembly is a separate and computationally demanding step that can fail or introduce errors, particularly in regions of repeated DNA that confuse alignment algorithms.
When researchers sequenced the axolotl (Ambystoma mexicanum), its genome of approximately 32 billion base pairs, roughly ten times the size of the human genome, made assembly one of the most demanding vertebrate projects attempted at the time. Assembling that genome required combining multiple sequencing technologies and produced an initial assembly with thousands of gaps that took years of follow-up work to reduce.
Genomic Library
/ jeh-NOH-mik LY-brer-ee / · Greek genea, birth; nomos; Latin libraria, collection
Genomic library is a collection of cloned DNA fragments that together represent the entire genome of an organism, with each fragment stored inside a vector and maintained in a host such as Escherichia coli.
To construct a genomic library, scientists digest an organism’s total DNA with restriction enzymes and ligate each fragment into a vector, commonly a plasmid, bacteriophage, or bacterial artificial chromosome. Each transformed bacterial colony or phage plaque harbors a single fragment, and the full collection of clones covers every region of the source genome at least once. Bacterial artificial chromosome libraries, widely used in large-genome projects, can carry inserts of 100 to 300 kilobases, making them far more efficient for covering complex genomes than plasmid-based libraries.
The Human Genome Project relied heavily on BAC libraries to organize and sequence the roughly 3.2 billion base pairs of the human genome.
Before the Human Genome Project began sequencing in earnest, researchers spent years constructing overlapping BAC libraries that physically mapped the human genome into ordered, manageable segments, a strategy called clone-by-clone sequencing that produced the first high-quality reference sequence by 2003.
A genomic library is a digital database of gene sequences. It is a physical collection of living bacterial clones or packaged phage particles, each carrying a real DNA fragment that researchers can grow, extract, and analyze.
Researchers constructing a genomic library from the domestic dog (Canis lupus familiaris) inserted size-selected fragments of approximately 150 kilobases into BAC vectors, generating roughly 200,000 clones to achieve ten-fold coverage of the 2.4-billion-base-pair genome. Screening that library with gene-specific probes allowed scientists to isolate and sequence individual loci linked to inherited diseases such as progressive retinal atrophy.