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Term used to represent various biological half-lives for a drug, including: (a) the kinetic or metabolic half-life, i.e. the time for the concentration of drug in plasma to decline to half its original level; (b) the half-life of the effect of a drug, i.e. the time necessary for the response to the drug to decline to half the original response.

Tab Separated Variable (TSV)

A form of file for holding scientific, or other, data. Data is listed in columns in a text file, each value being separated by a tab. Each new line represents a new set of data. This format is used mainly on Apple Macintosh computers whereas Windows based PCs tend to use the CSV format. (see Comma Separated Variable)

Tabes dorsalis

A syphilitic infection of the dorsal root ganglion.


A class of neuropeptides (i.e., peptides produced by cells of the nervous system; neurons). They include neurokinin A, neurokinin B, eledoisin, physalaemin, kassinin, substance P, and substance K. Some of these neuropeptides (e.g., Substance P) are picked up by mast cellslymphocytes, and/or monocytes; and cause those three types of immune system cells to release certain lymphokines (e.g., tumor necrosis factor, interleukin-1 etc.), thus activating the immune system.


A consensus sequence surrounding the lariat branch point of eukaryotic pre-mRNA introns and used during splicing.

Tactile defensiveness

Being overly sensitive to touch; withdrawing, crying, yelling or striking when one is touched. Not being able to tolerate being touched or touching things with texture.


A reduction in the response to an agonist while it is continuously present at the receptor, or a progressive reduction in the response upon repeated presentation of the agonist.

Tactual sign

A form of sign language in which signs are made while individuals face each other and hold hands to feel the movement.


A method of speech reading using touch, in which the consumer  places thumb on lips of the speaker, with fingers on throat (rarely used).

Tandem duplication

Adjacent identical chromosome segments.

Tandem repeat sequences

Multiple copies of the same base sequence on a chromosome; used as markers in physical mapping.


In geometry: A line that intersects a circle in one point. In a triangle: The side opposite an angle ÷ the side adjacent to the same angle.

Tangible Reinforcement Operant Conditioning Audiometry (TROCA)

A way to test a child's hearing by using a tangible item (candy or trinkets) that is pleasing to children as a reinforcer for appropriate responses. The item is presented each time the child presses the button when the sound is heard.

Tanner Stage

Medical term used for stages of puberty ranging on scale of 1-5.

Tap, Tapping

A tap is an instrument used to create threads holes in a hole drilled in bone. Tapping is process of using a tap to create the thread holes. Tapping is used for inserting screws in cortical bone. To insert a cortical screw, a pilot hole is first drilled in the bone that has the same diameter as the core diameter of a screw. The tap is then inserted creating the thread holes for the screw. Finally the screw is inserted. The type of screw inserted is called a nonself-tapping screws. See self-tapping screw.

Taq polymerase

A heat-stable DNA polymerase isolated from the bacterium Therrnus aquaticus, used in PCR. A DNA polymerase isolated from the bacterium Thermophilis aquaticus and which is very stable to high temperatures. It is used in PCR procedures and high temperature sequencing.

Tardive dyskinesia

A variable complex of choreiform or athetoid movements developing in patients exposed to antipsychotic drugs.  Typical movements include tongue-writhing or protrusion, chewing, lip-puckering, choreiform finger movements, toe and ankle movements, leg-jiggling, or movements of neck, trunk and pelvis. These movements may be either mild or severe and may occur along or in many combinations and permutations.

Targeted gene knockout

The introduction of a null mutation in a gene by a designed alteration in a cloned DNA sequence that is then introduced into the genome by homologous recombination and replacement of the normal allele.

Targeted mutagenesis

Deliberate change in the genetic structure directed at a specific site on the chromosome.  Used in research to determine the targeted region's function.

Task analysis

Breakdown of a particular job into its component parts; information gained from task analysis can be utilized to develop training curricula or to price a product or service.

TATA box

A sequence found in the promoter (part of the 5' flanking region) of many genes. Deletion of this site (the binding site of transcription factor TFIID) causes a marked reduction in transcription, and gives rise to heterogeneous transcription initiation sites. A DNA sequence (consensus TATAAA) at about minus 25 (ie. 25 nucleotides upstream of the transcription start site) in the promoter region of many eukaryotic genes involved in binding RNA polymerase via a TATA binding protein. Analogous to the Pribnow box in prokaryotes.

Tau protein

A protein that maintains the stability of the microtubules that serve as a transport system within brain cells. Abnormal aggregations of modified tau proteins are chief components of the neurofibrillary tangles found in the brains of patients with Alzheimer’s disease.

Tautomeric shift

The spontaneous isomerization of a nitrogen base to an alternative hydrogen-bonding form, possibly resulting in a mutation. Reversible shifts of proton position in a molecule. Bases in nucleic acids shift between keto and enol forms or between amino and imino forms.


A movement toward or away from a stimulus.

Taxon (Plural = Taxa)

Any named group of organisms, not necessarily a clade;    General term for a taxonomic group, i.e. speciesgenusfamily. A taxon may be designated by a Latin name or by a letter, number, or any other symbol. Taxa = The named classification unit (e.g. Homo sapiens, Homo, Hominidae, Primates or Mammalia) to which individuals, or sets of species, are assigned. Higher taxa are those above the species level.


The science of naming and classifying organisms; The naming and assignment of organisms to taxa; The classification of organisms according to their evolutionary relationship. The branch of biology concerned with naming and classifying the diverse forms of life. Taxonomic groups are organized in a hierarchical fashion from the most inclusive domains of life (archaea, bacteria, eukarya, viridae) to the lowest most specific species description (e.g. Homo sapiens).

Tay-Sachs disease

An inherited disorder caused by the absence of a vital enzyme called Hexosaminidase (hex-A) which results in the destruction of the nervous system. A baby who has Tay-Sachs develops normally for the first few months, then deterioration causing mental and physical disabilities begins.

T cells

A type of lymphocyte responsible for cell-mediated immunity that differentiates under the influence of the thymus.
See T lymphocytes

T cell lymphoma

A cancer of the lymphatic system where the cells that have become cancerous are a type of white blood cell called T Lymphocytes.

T Distribution

The t distribution (sometimes called Student's t distribution) is a statistical distribution which is used when a gaussian distribution is not applicable. The t distribution is a series of distributions which approach a gaussian distribution the larger the sample size but are more leptokurtic the smaller the sample size. The standard deviation of a t distribution with less than an infinite sample size is less than that of the gaussian distribution.


A portion of the Ti plasmid that is inserted into the genome of the host plant cell.


A part of a sum in an algebraic expression.

Terminating decimal

A fraction whose decimal representation contains a finite number of digits.

Teleological (teleology)

A way of arguing that natural systems have a way to look forward to improve their own situation. Teleological arguments are often found in evolutionary literature such as '... a plant becomes tastier in order to gratify the animal's needs and desires....' (see Pollan, 2008, In Defense of Food, p.102). Of course, plants to not plan on being tastier, but this 'tastiness' is the result of animals preferring this particular flavor increasing the seedling's chance to grow and have its own offspring.


An enzyme that adds telomeric sequences to the ends of eukaryotic chromosomes. No template is necessary. An enzyme that catalyzes the lengthening of telomeres; the enzyme includes a molecule of RNA that serves as a template for new telomere segments.


The ends of linear chromosomes; The protective structure at each end of a eukaryotic chromosome. Specifically, the tandemly repetitive DNA at the end of the chromosome's DNA molecule. These structures are required for replication and stability.


The fourth and final stage of mitosis or meiosis in which chromosomes uncoil; the spindle breaks down; and cytokinesis usually occurs.  The late stage of nuclear division when daughter nuclei re-form.

Temperate phage (or Terminal bacteriophage)

A bacterial virus that may become incorporated into the host-cell chromosome. A phage that can enter into lysogeny with its host. A phage that can become a prophage.

Temperate virus

A virus that can reproduce without killing the host.


A measure of the intensity of heat in degrees, reflecting the average kinetic energy of the molecules.

Temperature-sensitive mutant

An organism that has a wild-type phenotype at a permissive temperature but a mutant phenotype at a restrictive (non-permissive) temperature.


A pattern or mold guiding the formation of a negative or complementary copy.

Template strand (also known as antisense strand, non-coding strand)

The DNA strand that forms the template for both the transcribed mRNA and the coding DNA strand.

Temporal lobes

There are two temporal lobes, one on each side of the brain located at about the level of the ears.
These lobes allow a person to tell one smell from another and one sound from another. They also help in sorting new information and are believed to be responsible for short-term memory.
Right Lobe - Mainly involved in visual memory (i.e., memory for pictures and faces).
Left Lobe - Mainly involved in verbal memory (i.e., memory for words and names).

Temporomandibular joint syndrome

Complex of symptoms often seen in cervical sprain conditions.
Symptoms include clicking in the jaw on opening and closing the mouth, soreness in the jaw, headaches, buzzing sounds, changes in hearing, stiffness in the neck and shoulders, dizziness, and swallowing disorders.


A type of fibrous connective tissue that attaches muscle to bone: Cords of dense regular tissues that attach skeletal muscles to bone. The collagen fibers of tendons run along the longitudinal axis of the bone.


Long, flexible protrusions located about the mouth of many invertebrates; usually prehensile or tactile.

Tentorium cerebelli

The process of the dura mater between the cerebrum and cerebellum supporting the occipital lobes.


A drug or other agent that causes abnormal development.


A multi-layered benign tumor that grows from pluripotent cells injected into mice with a dysfunctional immune system. Used to test if a human embryonic stem cell (hESC) line has been established by injecting putative stem cells into mice and verifying that the resulting teratomas contain cells derived from all three embryonic germ layers.

Terminal redundancy

A linear DNA molecule with the same sequence (genetic information) at each end.
Terminal redundancy is seen in some phages (eg T2) and is generated because a phage head is capable of containing a DNA molecule larger than the complete genome and packaging of DNA into phage heads is determined by the headful. These phages also show circular permutation.

Terminal taxon

The taxa or named groups at the tips of the branches of a tree.

Termination codon

see Stop codon


A special sequence of nucleotides in DNA that marks the end of a gene. It signals RNA polymerase to release the newly made RNA molecule, which then departs from the gene.

Terminator sequence

A sequence in DNA that signals termination of transcription to RNA polymerase.
Not to be confused with terminator codons that are the stopping signal for translation.


Pertaining to land - as opposed to the water (aquatic) or the air (aerial).

Tertiary structure (of a protein)

The structure of an invididual protein chain (polypeptide) indicating the folding of the backbone (helical, extended, looping); The further folding of a protein bringing alpha-helices and beta-sheets into three-dimensional arrangements. The folding or coiling of the secondary structure to form a three-dimensional molecule. It results in irregular contortions of a protein molecule due to interactions of side chains involved in hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges.

Tertiary  wastewater treatment

selected biological, physical, and chemical separation processes to remove organic and inorganic substances that resist conventional treatment practices; the additional treatment of effluent beyond that of primary and secondary treatment methods to obtain a very high quality of effluent. The complete wastewater treatment process typically involves a three-phase process: (1) First, in the primary wastewater treatment process, which incorporates physical aspects, untreated water is passed through a series of screens to remove solid wastes; (2) Second, in the secondary wastewater treatment process, typically involving biological and chemical processes, screened wastewater is then passed a series of holding and aeration tanks and ponds; and (3) Third, the tertiary wastewater treatment process consists of flocculation basins, clarifiers, filters, and chlorine basins or ozone or ultraviolet radiation processes.


A hard shell produced by some unicellular protists; may be made of calcium carbonate, silica, or sand grains.

Test bias

Unfairness in a testing procedure or instrument that gives one group a particular advantage or another disadvantage, which may be due to matters unrelated to ability, such as culture, sex, or race.

Test cross

The crossing of an organism, with an unkown genotype, to an organism that is homozygous for one or more recessive alleles (tester), to determine the unknown genotype.  A cross between an individual of unknown genotype or a heterozygote (or a multiple heterozygote) to a homozygous recessive individual. The ratio of phenotypes in the offspring determines the unknown genotype.

Test for Auditory Comprehension of Language - Revised

A testing instrument designed to measure a child's understanding of grammar and sentence structure. Contains three subtests: Word Classes and Relations, Grammatical Morphemes, and Elaborated Sentences.

Testis (Plural = testes)

The male reproductive organ, or gonad, in which sperm and reproductive hormones are produced.

Testicular feminization syndrome

A human condition, inherited as an X-linked recessive, caused by a mutation in a gene coding for the androgen (testosterone) receptor, in which genetical (XY) males develop female secondary sexual characters.

Testis-determining factor (TDF)

General term for the gene determining maleness in human beings (Tdf in mice).

Test Method (in immunoassays)

A test method is an immunoassay procedure developed to measure a specific analyte.
The term test method encompasses the protocol specifications such as the type of curve fit selected and the number of unknown replicates, the reagents used in the assay runs, and all of the data generated from all of the assay runs of that test method. There can be more than one test method for a single analyte.

Test of Auditory Perceptual Skills (TAPS)

A testing instrument designed to measure auditory skills of children 4 - 12 years of age. Subtests are used to test different areas, with an age equivalent of years and months being scored as results. Subtest 1: Auditory Number Memory (forward and reversed) is a measure of ability to retain and repeat a number series. Language ages in years and months for digits forward and digits reversed are scored. Subtest 2: Auditory Sentence Memory taps a child's ability to remember and repeat sentences. Subtest 3: Auditory Word Memory measures the ability to repeat a word series in the same sequence presented. Subtest 4: Auditory Interpretation of Directions measures auditory memory and sequencing and the ability to understand and interpret what is heard. Subtest 5: Auditory Word Discrimination assesses a child's ability auditorally to discriminate like pairs of words. Subtest 6: Auditory Processing measures the child's ability to understand a question and formulate a response.


A steroid, androgen hormone and the primary male sex hormone; the most abundant androgen hormone in the male body. It is produced by the testes in men and ovaries in women, and plays key roles in libido, energy, and immune function in both men and women.

Tetanus (in activity)

(1) A sustained burst of activity.
(2) The maximal, sustained contraction of a skeletal muscle, caused by a very fast frequency of action potentials elicited by continual stimulation.
Tetanus is used to describe a rapid and sustained burst of electrical stimuli applied to a nerve or a tissue.  In the context of muscle contractions, tetanus is used to describe the large maintained contraction of a skeletal muscle that occurs in response to a rapid and sustained burst of Action Potentials in the motor nerve innervating the muscle.  The APs occur so rapidly that the individual muscle twitches to each AP sums up to give a large and sustained contraction.  If this sustained contraction is smooth without any fluctuations of the individual twitches being evident, it is referred to as fused tetanus; if there are fluctuations in the overall sustained contraction, it is unfused tetanus.

Tetanus (medical: also known as Lockjaw)

A non-contagious disease caused by germs found in the soil which occurs as often in adults as in children, enters the body through wounds, and which can cause muscle spasms, severe nervous system damage, or death. Immunization with the DTP vaccine protects infants and children against this disease. Reimmunization is recommended every ten years.

Tethered particle motion (TPM)

A tiny plastic bead < 1 micrometer (mm) in diameter is attached to the end of a DNA molecule. Then by computer analysis of the bead movements seen in a microscope, it is possible to monitor the DNA as it looped and unlooped, revealing details of the molecule's behaviour. A technique pioneered at Brandeis University to look at single molecules of DNA.


(1) Four homologous chromatids in a bundle in the first meiotic prophase and metaphase.
(2) The four haploid product cells from a single meiosis.

The meiotic configuration of four chromatids first seen in pachytene. There is one tetrad per pair (bivalent) of homologous chromosomes.

Tetrad analysis

The use of tetrads (definition 2 above) to study the segregation of chromosomes and genes during meiosis.

Tetraparental mouse

A mouse that develops from an embryo created by the experimental fusion of two separate embryos (blastulas) from matings of different parents.


(1) A cell having four chromosome sets, or (2) an organism composed of such cells.


Four legged


A unicellular sporangium containing four asexual tetraspores which are produced from meiosis. Tetrasporangia are found in certain red algae.


A tetrad containing four different genotypes, two parental and two recombinant. A spore arrangement in Ascomycetes that consists of two parental and two recombinant spores indicating a single crossover between two linked loci.

Text file

1. In computer usage, any file written in pure character format . Sometimes called a "plain text file."
2. In a data library situation, "text file" may also refer to a file containing natural language text (e.g., a literary text such as the works of Shakespeare) as opposed to a numeric data file that contains mostly numbers. Such a file could be stored as a character format file but does not necessarily have to be. Also known as a character file.


One of two integrating centers of the vertebrate forebrain. Neurons with cell bodies in the thalamus relay neural input to specific areas in the cerebral cortex and regulate what information goes to the cerebral cortex. The thalamus has been described as a searchlight that helps focus attention on specific events in the world.


Drug which is a powerful human teratogen. First synthesized in Germany in 1954 as a new antihistamine, the drug was found to be a safe and effective sedative. It was widely used beginning in 1958 to relieve symptoms of morning sickness and nausea in pregnancy (although never approved in the US). By the 1960's the teratogenic effects of the drug had become apparent; the most common birth defects included severe limb abnormalities and malformed internal organs.

Theca (Plural = thecae)

General term for any stiff outer covering of a unicellular protist, and usually made up of interlocking plates.  A layer which encloses a body, may refer to a closely adpressed rigid wall, or to a more loosely-attached rigid lorica or test or even to a soft enclosing sheath of material.  Dinoflagellates and diatoms are examples of protists with thecae.


A statement that has been proven.


A generalization based on many observations and experiments; a verified hypothesis.
A scientific theory is an established and experimentally verified fact or collection of facts about the world. Unlike the everyday use of the word theory, it is not an unproved idea, or just some theoretical speculation. The latter meaning of a 'theory' in science is called a hypothesis.

Therapeutic bronchoscopy

A bronchoscopy procedure that is performed to remove secretions, mucous plugs, or foreign bodies

Therapeutic cloning

The process of using somatic cell nuclear transfer (SCNT) to produce cells that exactly match a patient. By combining a patient's somatic cell nucleus and an enucleated egg, a scientist may harvest embryonic stem cells from the resulting embryo that can be used to generate tissues that match a patient's body. This means the tissues created are unlikely to be rejected by the patient's immune system.

Therapeutic index

(or therapeutic ratio). The ratio of the toxic dose of the drug to the dose which causes the desired therapeutic effect.

thermal pollution

a reduction in water quality caused by increasing its temperature, often due to disposal of waste heat from industrial or power generation processes. Thermally polluted water can harm the environment because plants and animals can have a hard time adapting to it.

Thermal (pressure or electric field) resistance constant (z)
z(T) [z(P) or z(E)]

The temperature (°C)  (pressure or electric field) increase needed to accomplish a one-log cycle reduction in the D-value.


The physical theory of heat and energy distribution in the universe; The study of transformations of energy. The first law of thermodynamics states that, in all processes, the total energy of a system plus its surroundings remains constant, and that energy cannot be made nor destroyed. The second law states that all natural processes tend to proceed in such a direction that the disorder or randomness (the entropy) of the system increases.

thermoelectric power water use

water used in the process of the generation of thermoelectric power. Power plants that burn coal and oil are examples of thermoelectric-power facilities.\


Microorganisms that grow best at temperatures above 110° F (43° C).

Thermophysical properties

Properties that influence the heating rate of a material.
Examples of thermophysical properties are thermal conductivity (the ability of the material to conduct heat), specific heat (the ability of the material to store heat), and density (the mass per unit volume of the material).


The maintenance of internal temperature within a tolerable range.


A form adopted by some species of ciliates that typically does not feed but moves quickly. May be thought of as an adaptation in response to a lack of food and the task of which is to hunt out new sources of food.

Theta structure

An intermediate structure formed during the replication of a circular DNA molecule.

Thickeners (of food)

Used to increase viscosity, modify texture and impart stability.

Thick filament

A filament composed of staggered arrays of myosin molecules; a component of myofibrils in muscle fibers.


Surgical puncture and drainage of the pleural cavity. Also called pleurocentesis or thoracocentesis

Thoracic-abdominal breathing

A respiratory pattern characterized by expansion of the thoracic and upper abdominal areas on inhalation. The rib cage elevates as it expands laterally and in the anterior-posterior dimension, while the diaphragm contracts and lowers, creating expansion vertically; intermittently evident as early as 7 to 8 months of age as in the abdominal obliques and intercostals become active in the respiratory process.


Surgical operation to open the chest cavity.  Done to operate on the lungs.


(1) In vertebrates, that portion of the trunk containing the heart and lungs.
(2) In crustaceans and insects, the fused, leg-bearing segments between head and abdomen.

Three-point testcross

A testcross involving one parent with three heterozygous gene pairs and another (tester) with three homozygous recessive gene pairs.


Describes the operation of setting values below a given threshold to zero. This may concern all pixels in an image, or amplitudes in a digital signal. Sometimes, the term implies that values above the threshold are set to one, creating a binary image or signal. Thresholding is often applied to suppress noise, in situations where the signal-to-noise ratio is large. If a high fraction of channels contains only low-amplitude noise, thresholding produces sparse information and may be a powerful step towards data compression. Thresholding with some very simple encoding scheme, like transmitting the sparse channels along with their channel number, is often referred to as zero suppression .

Threshold of discomfort (in hearing)

An uncomfortable loudness level. The minimum loudness level, often for speech, that the listener designates as uncomfortable.

Threshold potential

The potential an excitable cell (neuron or muscle) membrane must reach for an Action Potential to be initiated.


Similar to PEL above but are not legal standards for human exposure. Determined and published by the American Conference of Government Industrial Hygienists (ACGIH).


A lower than normal number of platelets (blood cells that play an important role in clotting and bleeding) in the blood. Low platelet counts, thrombocytopenia, can be caused by a variety of reasons. In general, they can be divided into: (a) decreased platelet production, (b) increased platelet destruction or consumption, or (c) increased splenic sequestration (capturing of circulating platelets in the spleen).


The process that occurs when a piece of a thrombus (clot) breaks off. The broken off piece, called an embolus, may move through the circulation and eventually block a smaller vessel far from where it originally formed.


A clot inside a blood vessel. See Embolus


Fungus infection which usually affects the mouth or vagina. White patches appear and the surrounding skin is red and sore. Occurs most often in people with low resistance to infection (e.g. after chemotherapy) or in areas that have been treated with radiotherapy (e.g. in the mouth).


A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.

Thymidine kinase

An enzyme that allows a cell to utilize an alternate metabolic pathway for incorporating thymidine into DNA. Used as a selectable marker to identify transfected eukaryotic cells.


A nitrogenous base, one member of the base pair A- T (adenine- thymine).

Thymine dimmer

A pair of abnormally chemically bonded adjacent thymine bases in DNA, resulting from damage by ultra-violet irradiation. The cellular processes that repair this lesion often make errors that create mutations.

Thymus gland

A hormone-producing structure located in the neck region of mammals (in the chest just behind the sternum). Active in establishing the immune system; secretes several messengers, including thymosin, that stimulate T cells. Hormones produced by this gland stimulate the production of certain infection-fighting cells, and plays a central role in the development of T cells of the immune system.

Thyroid gland

A hormone-producing structure located inside the neck.
It regulates the body's ability to break down food and convert it to energy.
It secretes iodine-containing hormones (T3 and T4), which stimulate metabolism and influence development and maturation in vertebrates, and calcitonin, which lowers blood calcium levels in mammals.
Thyroid disorders result from too little or too much thyroid hormone. Symptoms of hypothyroidism (too little hormone) include decreased energy, slow heart rate, dry skin, constipation, and feeling cold all the time.

Thyroid-stimulating hormone (TSH, Thyrotropin)

A hormone that stimulates the thyroid to secrete the hormones thyroxine and triiodothyronine. A hormone produced by the anterior pituitary that regulates the release of thyroid hormones.

Tic douloureux

Excruciating episodic pain in the dermatome of the trigeminal nerve often precipitated by gentle stimulation of certain trigger points. Also known as Trigeminal neuralgia

Tidal volume.

The amount of air which enters and leaves the lungs during one regular breath.  This is measured with a device called a Peak flow meter.

Tight junction

A type of intercellular junction in animal cells that prevents the leakage of material between cells.

Time-Delayed Fluorescence

Time-delayed fluorescence is a technique in which the fluorescence of slowly emitting compounds, such as metal chelates, is measured.

Time-of-flight spectrometer

A type of mass spectrometer that measures the time it takes for an ion of known electrical change, but unknown mass, to reach a detector at a known distance in order to determine the mass-to-charge ratio of the particle.

Time series

Observations of a variable made over time. Time series, of a sort, can also be constructed from a cross sectional study if the same questions are asked more than once over time.


High-pitched throbbing or ringing sounds in the ear, usually heard only by the affected person. Tinnitus is commonly caused by disease of the inner ear but may also involve central nervous system, structures.

Ti plasmid

A plasmid of a tumor-inducing bacterium that enables the bacterium to infect plant cells and produce a tumour (crown gall tumour). A circular plasmid of Agrobacterium tumefaciens that integrates a segment of its DNA into the host chromosome of a plant; frequently used as a carrier for genetic engineering in plants.


An integrated group of cells with a common structure and function.

Tissue culture

A procedure for growing or cloning enough cells through in vitro techniques to make a tissue. A technique in which portions of a plant or animal are grown on an artificial culture medium. (Also: in vitro culture.)

Tissue-specific expression

Gene function which is restricted to a particular tissue or cell type. For example, the glycoprotein hormone alpha subunit is produced only in certain cell types of the anterior pituitary and placenta, not in lungs or skin; thus expression of the glycoprotein hormone alpha-chain gene is said to be tissue-specific. Tissue specific expression is usually the result of an enhancer which is activated only in the proper cell type.


The dilution factor used to bind a specific ligand concentration range.

Titratable acid

Measure of titratable hydrogen ions. Includes H+ ions free in solution and those associated with acids and proteins.


Method of accurately adding one liquid to another, commonly used in food analysis.
Hence Titration curve = A plot of the pH versus the equivalents of base added during titration of an acid.

T lymphocyte

Type of white blood cell, produced in the bone marrow.  Lymphocytes make up a quarter to a third of the white blood cells. Then there are two types of lymphocytes, B and T cells. The T lymphocytes help the B cells make antibodies as part of the immune response, to fight bacterial infections. They also are instrumental in rejection of foreign tissue, and may be important in the body's defense against cancer.


The melting point for a double-stranded nucleic acid. Technically, this is defined as the temperature at which 50% of the strands are in double-stranded form and 50% are single-stranded, i.e. midway in the melting curve. A primer has a specific Tm because it is assumed that it will find an opposite strand of appropriate character.


A long-lasting, almost permanent, level of activity. Used to describe the phase of a grand mal seizure that is marked by prolonged muscular contraction (rigidity).

Tonic bite reflex

A common abnormal feeding pattern; the jaw moves upward into a tightly clenched posture when the teeth are stimulated by a finger, spoon or other object.
This makes it difficult for the child to open his/her mouth.


An operational description of the consequences to animal cells of the movement of water into or out of them.
Tonicity tells us how a solution affects a cell because of water movement
– i.e., if you place cells in that solution do they swell, or shrink, or not be affected at all?
Tonicity depends on the effective [Non-penetrating particles] in a solution because if the particles don’t penetrate & are at unequal [ ] in the cell versus the solution, then water will move and affect cell volume (since animal cells have a rigid shape are less able to accommodate volume changes).
Iso-tonicity: Generally the intra-cellular [Non-penetrating particles] creates an osmotic pressure of ~280 mOsmolar (mOsm). So if extracellular [NPP] osmotic pressure = ~280 mOsm, then there will be no net water movement into or out of the cell and this solution is isotonic to that cell.
Hypo-tonicity: If extracellular [NPP] osmotic pressure < ~280 mOsm, then there will be a net water movement into the cell as the extracellular solution has a higher [Water].  This solution is hypotonic to that cell.
Hyper-tonicity: If extracellular [NPP] osmotic pressure > ~280 mOsm, then there will be a net water movement out the cell as the extracellular solution has a lower [Water].  This solution is hypertonic to that cell.


Topological form of DNA with the same sequence as another but differing in linking number (supercoiling). And Topoisomerase = Enzymes of two types that can remove (or create) supercoiling in duplex DNA by creating transitory breaks in one (type I) or both (type II) strands of the sugar-phosphate backbone.


In animals, a physiological state that conserves energy by slowing down the heart and respiratory systems.


The tendency of a body to rotate under an applied force.

Total error

Total error is composed of random error, which is the error attributable to chance, and systematic error, which is the error attributable to changes in the test method.

Total testosterone

The total amount of testosterone in the blood, combining free testosterone and testosterone bound to certain molecules and already at use in the body.


Having the ability to give rise to all the cell types of the body plus all of the cell types that make up the extraembryonic tissues such as the placenta.
(See MultipotentPluripotent)

Trace element

An element indispensable for life but required in extremely minute amounts.


The tracer is a ligand or binder which has been attached to a measurable label.

Tracer Activity

The tracer activity samples are baseline standards which measure the activity of the tracer label without a ligand-binder factor. The tracer, substrate, and buffer measured in the tracer activity samples are taken from the same sources that are used for the rest of the same assay run. The tracer activity samples from isotopic tests are sometimes termed total count samples. Isotopic tracer activity samples contain the same amount of tracer that is added to each assay sample and are therefore higher in activity than any other sample. Nonisotopic tracer activity samples might not have the highest activity of all samples if, for example, the enzyme/substrate mixture must be diluted to be measured. The bound raw response is then used to calculate the adjusted, normalized and y-axis responses. The variation in the tracer activity raw response from assay to assay is a measure of the label response variation. Label response variation is caused by anything which affects the raw response, such as instrument drift, enzyme/substrate deterioration, and isotopic decay, that is not related to changing conditions in the ligand-binder reaction.


The windpipe. The portion of the respiratory tube that has C-shaped cartilagenous rings and passes from the larynx to two bronchi.


The windpipe. The portion of the respiratory tube that has C-shaped cartilagenous rings and passes from the larynx to two bronchi.

Tracheal sysem

A gas exchange system of branched, chitin-lined tubes that infiltrate the body and carry oxygen directly to cells in insects.


A temporary surgical opening at the front of the throat providing access to the trachea or windpipe to assist in breathing.


A group or bundle of nerve fibers’ axons, with accompanying connective tissue, located within the central nervous system and running within it..


A physical characteristic brought about by the expression of a gene or many genes; The physical or metabolic phenotype of an organism such as red flower color and length of stem in plants and black fur or pink eye in mice. Examples of traits are height, eye color, and the ability to roll your tongue. Variations in these characteristics are dependent upon the particular alleles an individual has for the genes determining the trait.

Trait ratio

An expression of an animals performance for a particular trait relative to the herd or contemporary group average. It is usually calculated for most traits as: (indiviual record / Average of animals in group) * 100


The path that a body makes as it moves through space.

Trans conformation

In a heterozygote involving two mutant sites (ab) within a gene or gene cluster, the arrangement, Ab/aB.


A transcript is an RNA copy of a DNA template, i.e., a ribonucleic acid copy of a gene. Transcripts are also known as messenger RNA and are the mediator between the gene and a protein product.


The synthesis of RNA using a DNA template; The process of copying DNA to produce an RNA transcript. The process whereby RNA is synthesized from a DNA template; it is the first step in gene expression. The resulting RNA, if it codes for a protein, will be spliced, polyadenylated, transported to the cytoplasm, and by the process of translation will produce the desired protein molecule

Transcription factor

A protein which is involved in the transcription of genes. These usually bind to DNA as part of their function (but not necessarily). A transcription factor may be general (i.e. acting on many or all genes in all tissues), or tissue-specific (i.e. present only in a particular cell type, and activating the genes restricted to that cell type). Its activity may be constitutive, or may depend on the presence of some stimulus; for example, the glucocorticoid receptor is a transcription factor which is active only when glucocorticoids are present.

Transcription Mediated Amplification (TMA)

A target nucleic acid amplification method that uses RNA transcription (RNA polymerase) and DNA synthesis (reverse transcriptase) to produce RNA amplicon from a target nucleic acid. TMA can be used to target both RNA and DNA.
TMA has several other differences in comparison to PCR and LCR:
- TMA is isothermal. A water bath or heat block is used instead of a thermal cycler.
- TMA produces RNA amplicon rather than DNA amplicon. Since RNA is more labile in the laboratory environment than DNA, this helps reduce the possibility of carry-over contamination.
- TMA produces 100-1000 copies per cycle in contrast to PCR and LCR that produce only two copies per cycle. This results in a 10 billion fold increase of copies within about 15-30 minutes.


Tempero-mandibular joint, the joint that hinges the lower jaw (mandible) to the skull.


The transcriptome is a term used to indicate the total set of all the mRNA (the “transcripts”) found at any given time in a cell or organism. Since messenger RNA (mRNA, the transcript or copy of a DNA template) are the mediator between the gene and a protein product, the presence of mRNA in a cell indicates the use of a gene. The type and number of active genes is an indicator of the actual metabolic and physiological state of a cell.


Process of transport of substance across an epithelium by uptake into and release from coated vesicles

Transdermal delivery

A method of delivering medications through the skin.  It may be accomplished through patches that can be worn for varying lengths of time or as an ointment that can be applied manually.


The process by which stem cells from one tissue differentiate into cells of another tissue.


A device that receives energy from one system and retransmits it to another, often in a different form.

Transducing particle

A defective phage carrying part of the host genome in place of part of the phage genome.


(1) The transfer of genetic material (DNA) from one cell to another by a virus.
(2) The process of conversion of the physical energy of a sensory stimulus (light, sound, pressure) into a biological response in a receptor cell.

Trans fats

Occur naturally in beef, butter, milk and lamb fats and in commercially prepared, partially hydrogenated margarines and solid cooking fats. The main sources of trans fats are margarine, shortening, commercial frying fats and high-fat baked goods.
Partially hydrogenated vegetable oils were developed in part to help displace highly saturated animal and vegetable fats used in frying, baking and spreads. However, trans fats, like saturated fats, may raise blood LDL cholesterol levels (the so-called "bad" cholesterol) - but not as much as the saturates do. At high consumption, levels may also reduce the HDL or "good" cholesterol levels.


The process by which exogenous DNA in solution is introduced into cells; A method by which experimental DNA may be put into a cultured mammalian cell.
The introduction of foreign DNA into eukaryotic or prokaryotic cells. Such experiments are usually performed using cloned DNA containing coding sequences and control regions (promoters, etc) in order to test whether the DNA will be expressed. Since the cloned DNA may have been extensively modified (for example, protein binding sites on the promoter may have been altered or removed), this procedure is often used to test whether a particular modification affects the function of a gene.


The unconscious assignment to others of feelings and attitudes that were originally associated with important figures (parents, siblings, etc.) in one's early life. Transference may be negative (hostile) or positive (affectionate). The transference relationship follows the pattern of its prototype can be utilized as a therapeutic tool to help the patient understand emotional problems and their origins.

Transfer operon (tra)

Operon containing genes that produce the male (F- pili producing) bacterial phenotype.  The F+(plus) cell (male cell) can transfer the fertility factor (F plasmid) to an F-(minus) (female) cell.

Transfer RNA (tRNA)

Small RNA molecules that carry amino acids to the ribosome for polymerization into a polypeptide. An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA.A class of RNA having structures with triplet nucleotide sequences that are complementary to the triplet nucleotide coding sequences of messenger RNA (mRNA). The role of tRNAs in protein synthesis is to bond with amino acids and transfer them to the ribosomes, where proteins are assembled according to the genetic code carried by mRNA. During translation the amino acid is inserted into the growing polypeptide chain when the anticodon of the tRNA pairs with a codon on the mRNA being translated.

Transform (in microbiology or oncology)

(1) In microbiology and genetics the modification of of one genotype by the external application of DNA from a cell of another genotype.
(2)In oncology (the study of cancer formation) the conversion of a normal cell into a cancerous one by mutation or transfection.
Occurs from the incorporation of the genetic material of an individual cell by incorporation of exogenous DNA into its genome.


In prokaryotes, a cell that has been genetically altered through the uptake of foreign DNA. In higher eukaryotes, a cultured cell that has acquired a malignant phenotype.


A change in the genetic structure of an organism as a result of the uptake and incorporation of foreign DNA.

Transformation (with respect to bacteria)

The process by which a bacteria acquires a plasmid and becomes antibiotic resistant.
This term most commonly refers to a bench procedure performed by the investigator which introduces experimental plasmids into bacteria.

Transformation (of cultured cells)

A change in cell morphology and behavior which is generally related to carcinogenesis. Transformed cells tend to exhibit characteristics known collectively as the "transformed phenotype" (rounded cell bodies, reduced attachment dependence, increased growth rate, loss of contact inhibition, etc). There are different "degrees" of transformation, and cells may exhibit only a subset of these characteristics. Not well understood, the process of transformation is the subject of intense research.

Transformed Data

Transformed data are data which has been converted mathematically in order to better fit certain statistical or mathematical models.


A device that changes the voltage of electricity.

Transformer gene

An allele in fruit flies (Drosophila) that converts chromosomal females into sterile males.

Transforming oncogene

A gene that upon transfection converts a previously immortalized cell to the malignant phenotype.


Organisms that have had foreign DNA stably integrated into their genome. Having artificially altered genetic material. A transgenic organism is one that has had its genotype altered by the introduction of a gene or DNA sequence into its genome by genetic manipulation; the introduced gene or DNA segment is called a transgene.

Transgenic mouse

A mouse which carries experimentally introduced DNA. The procedure by which one makes a transgenic mouse involves the injection of DNA into a fertilized embryo at the pro-nuclear stage. The DNA is generally cloned, and may be experimentally altered. It will become incorporated into the genome of the embryo. That embryo is implanted into a foster mother, who gives birth to an animal carrying the new gene. Various experiments are then carried out to test the functionality of the inserted DNA.

Transient diploid

The stage of the life cycle of predominantly haploid fungi (and algae) during which meiosis occurs.

Transient transfection

When DNA is transfected into cultured cells, it is able to stay in those cells for about 2-3 days, but then will be lost (unless steps are taken to ensure that it is retained).
During those 2-3 days, the DNA is functional, and any functional genes it contains will be expressed. Investigators take advantage of this transient expression period to test gene function.


A type of nucleotide-pair substitution involving the replacement of a purine with another purine, or of a pyrimidine with another pyrimidine, e.g., GC with AT.
Hence Transition mutation = A mutation in which a purine/pyrimidine base pair is replaced with a base pair in the same purine/pyrimidine relationship eg. GC with AT.

Transition-state intermediate

In a chemical reaction, an unstable and high-energy configuration assumed by reactants on the way to making products. Enzymes are thought to bind and stabilize the transition state, thus lowering the energy of activation needed to drive the reaction to completion.

Transitive property

The property that states that if a = b, and b = c, then a = c.


In molecular biology: The process of protein synthesis whereby the primary structure of the protein is determined by the nucleotide sequence in mRNA; The process of decoding a strand of mRNA, thereby producing a protein based on the code.
In geometry: A shift of the axes of the Cartesian Coordinate System.
In molecular biology: The ribosome-mediated production of a polypeptide whose amino acid sequence is derived from the codon sequence of an mRNA molecule. This process requires ribosomes (which are composed of rRNA along with various proteins) to perform the synthesis, and tRNA to bring in the amino acids. Sometimes, however, people speak of "translating" the DNA or RNA when they are merely reading the nucleotide sequence and predicting from it the sequence of the encoded protein. This might be more accurately termed "conceptual translation".

Translocase (EF-G)

Elongation factor in prokaryotes necessary for proper translocation at the ribosome during the translation process. Replaced by eEF2 in eukaryotes.


1. An aberration during meiosis causing the relocation (switching) of a chromosomal segment in a different position in the genome. A chromosomal configuration in which part of a chromosome becomes attached to a different chromosome.
2. During protein synthesis, the third stage in the elongation cycle when the mRNA carrying the growing polypeptide is shifted one codon (moves from the A site to the P site) on the ribosome.
3. A type of Down Syndrome in which a portion of the twenty-first chromosome pair breaks off and fuses with another pair.
4. The transport via phloem of food in a plant.
1. An aberration in chromosome structure resulting from an error in meiosis or from mutagens; attachment of a chromosomal fragment to a nonhomologous chromosome.
2. During protein synthesis, the third stage in the elongation cycle when the RNA carrying the growing polypeptide moves from the A site to the P site on the ribosome.

Transmembrane protein

A protein that spans the plasma membrane of a cell. Often the extracellular domain of the protein has the ability to bind to a ligand and the intracellular domain has an activity (such as a protein kinase) that can be altered (either increased or decreased) upon ligand binding.


the capacity of a rock to transmit water under pressure. The coefficient of transmissibility is the rate of flow of water, at the prevailing water temperature, in gallons per day, through a vertical strip of the aquifer one foot wide, extending the full saturated height of the aquifer under a hydraulic gradient of 100-percent. A hydraulic gradient of 100-percent means a one foot drop in head in one foot of flow distance.


A membrane protein that functions as an ion channel, solute transporter, facilitator or pump to move molecules across cell membranes.

Transposon or Transposable gene (also called a jumping gene)

A transposable genetic element; a mobile segment of DNA that can move from one location in the gene and reinsert at another site and serves as an agent of genetic change; DNA fragments incorporated into the chromosomal DNA.
A stretch of DNA containing one or more genes which, unlike most genes that remain fixed, can move from one part of the genome to another part because they can copy and insert themselves at many different sites within chromosomes. These rearrangements of physical location of DNA strands affect number, location, and sequence of genes coding for proteins and RNA, and are vital for generating mutations important for evolutionary fitness of an organism. Transposons contain a gene producing an enzyme that catalyzes insertion of the transposon at a new site. They also have repeated sequences that are 20-40 nucleotides in length at each end. Insertion sequences are short (600-1500 base pairs long) simple transposons that do not carry genes beyond those essential for insertion of the transposon. Complex transposons are much larger and carry additional genes. Genes incorporated in a complex transposon are known as jumping genes. Often the complex transposons are flanked by simple transposons. (see Non-coding sequences or Jumping genes)

Transposable elements

A general term for any genetic unit that can insert into a chromosome, exit, and relocate; includes insertion sequences, transposons, some bacteriophages, and controlling element. A region of the genome, flanked by inverted repeats, a copy of which can be inserted at another place. Often this term is used interchangeably with Transposon.


The movement of a DNA segment within the genome of an organism.


process by which water that is absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface, such as leaf pores. See process by which water that is absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface, such as leaf pores. See evapotranspiration.

Transtracheal catheter

A specialized catheter that is surgically inserted into the trachea (second cartilaginous ring) for the administration of low flow oxygen

Transurethral resection of the prostate (TURP)

A surgical procedure to cure Benign prostatic hypertrophy. An instrument inserted through the penile urethra is used to partially cut away the prostate to relieve obstruction of the urinary tract that occurs in Benign prostatic hypertrophy.


A line that intersects two other lines.

Transverse presentation

A situation in which the fetus lies across the birth canal.


A type of nucleotide-pair substitution involving the replacement of a purine with a pyrimidine, or vice versa for example GC with TA. Hence Transversion mutation = A mutation in which a purine/pyrimidine replaces a pyrimidine/purine base pair or vice versa eg. GC with TA.


A quadrilateral that has exactly two sides parallel.

Triangle test

Sensory analysis of samples in order to determine slight differences in single or complex sensory impressions.  Samples are arranged in the shape of a triangle; the aim is to tell which sample differs from the other two identical samples.


A quivering, involuntary movement of a part or parts of the body.


something that is very valuable to you.  Could be your pet dog, pirate's loot, or a pot of gold.

Triceps skinfold thickness

Measurement of subcutaneous fat located around the triceps.


Organelle in ciliates and dinoflagellates which releases long filamentous proteins when the cell is disturbed. A type of extrusome which, when extruded, takes the form of a fine stiff filament. Typical of Paramecium, but used inadvertently to refer to other types of extrusomes.  Used as a defense against would-be predators.


The constituent of fat composed of glycerol and three fatty acids.  Most triglycerides are obtained from food as fats or synthesized by the liver and stored in liver and fat cells (adipocytes). Triglycerides are one of three major sources of metabolic fuel (the other sources are carbohydrates and proteins) providing energy for the physiological processes of the body.


An organism heterozygous at three loci. Hence Trihybrid cross = a cross looking a three different characters: AaBbCc X AaBbCc


A polynomial with exactly three terms.


Possessing three germ layers: the endoderm, mesoderm, and ectoderm. Most eumetazoa are triploblastic.


Paralysis that involves three appendages, usually both legs and one arm.


The three nucleotide pairs that compose a codon. A set of three-nucleotide-long words that specify the amino acids for polypeptide chains.

Triplet code

A set of three-nucleotide-long words that specify the amino acids for polypeptide chains.


A cell having three chromosome sets, or an organism composed of such cells.


A diploid cell with an extra chromosome. Basically a diploid with an extra chromosome of one type, producing a chromosome number of the form 2n + l. It is caused by nondisjunction during cell division

Trisomy 21 (Also called nondisjunction)

A type of Down Syndrome in which the chromosomal pairs do not separate properly as the sperm or egg cells are formed, resulting in an extra chromosome on the twenty-first pair. The state of a cell or individual that has three chromosomes instead of two for a given pair. There are three common kinds of trisomy: trisomy 13 (Patau syndrome), trisomy 18 (Edward syndrome) and trisomy 21 (Down syndrome).


Transfer RNA; one of a class of rather small RNAs used by the cell to carry amino acids to the enzyme complex (the ribosome) which builds proteins, using an mRNA as a guide.


An organism that is an obligate inhabitant of caves and underground water systems.
Subterranean life often results in a series of characteristic morphological and physiological adaptations (troglomorphies) such as loss of pigment, blindness, and elongation of appendages.


Morphological characteristics often exhibited by troglobites due to adaptation to life in caves and subterranean water systems. Examples include blindness, a loss of skin pigment, and elongation of appendages.


The outer layer of the pre-implantation embryo in mice. It contains trophoplasm cells.


Said of organisms which are active and feeding, and contrasts with the encysted state, theronts, or swarmers. May also be used to refer to those aspects of metabolism associated with growth.

Trophic level

The division of species in an ecosystem on the basis of their main nutritional source.
The trophic level that ultimately supports all others consists of autotrophs, or primary producers.

Trophic strutcure

The different feeding relationships in an ecosystem that determine the route of energy flow and the pattern of chemical cycling.


The outer cell layer of the blastocyst, which forms the fetal part of the placenta.
It is responsible for implantation and develops into the extraembryonic tissues, including the placenta, and controls the exchange of oxygen and metabolites between mother and embryo.


Pertaining to behavior or action brought about by specific stimuli. For example, phototropic ("light-oriented") motion, gonadotropic ("stimulating the gonads") hormone.

Tropic hormone

A hormone that has another endocrine gland as a target.

Truncation selection

A breeding technique in which individuals in whom quantitative expression of a phenotype is above or below a certain value (the truncation point) are selected as parents for the next generation.


The precursor form of the pancreatic enzyme trypsin or a zymogen. It is found in pancreatic juice, along with amylase, lipase, and chymotrypsinogen. It is activated by enterokinase, which is found in the intestinal mucosa, to form trypsin. Once activated, the trypsin can activate more trypsinogen into trypsin. Serum trypsinogen is measured using a blood test. High levels are seen in acute pancreatitis, and cystic fibrosis.

T test

The t test is a statistical test which computes the probability (p) that two groups of a single parameter are members of the same population. The population must follow a t distribution. However, a t test is robust enough to allow considerable deviation from normality.

T tubules

A dense interconnecting network of tubules extending throughout the muscle cell cytoplasm. Formed by invaginations of the muscle cell plasma membrane (sarcolemma).  They are contiguous with the extracellular fluid.  They allow muscle Action Potentials to be conducted over the sarcolemma and deep into the muscle fibre, thereby allowing for rapid and coordinated excitation of the muscle cell.  The excitation of the T tubule is coupled to Ca+2 release from sarcoplasmic reticulum stores and Ca+2 release leads to contraction of the myofibrils.

Tuberous sclerosis

A birth defect that does not appear until late childhood, is related to mental retardation in about 66 percent of the cases, and is characterized by tumors on many organs.


A mass that forms within otherwise normal tissue, caused by the uncontrolled growth of a transformed cell. An abnormal mass of tissue. Tumors are a classic sign of inflammation, and can be benign or malignant (cancerous). There are dozens of different types of tumors. Their names usually reflect the kind of tissue they arise in, and may also tell you something about their shape or how they grow. For example, a medulloblastoma is a tumor that arises from embryonic cells (a blastoma) in the inner part of the brain (the medulla). Diagnosis depends on the type and location of the tumor. Tumor marker tests and imaging may be used; some tumors can be seen (for example, tumors on the exterior of the skin) or felt (palpated with the hands).

Tumor Necrosis Factor (TNF)

cytokine that is produced by macrophages (TNF-α) and some T cells (TNF-β).
This cytokine can exert a direct toxic effect on neoplastic cells. It has an antineoplastic effect but causes inflammation (as in rheumatoid arthritis).

Tumor Suppressor Gene

gene whose protein products inhibit cell division, thereby preventing uncontrolled cell growth (cancer); A gene encoding a protein that suppresses tumour formation; A gene that normally prevents unlimited cell division.  When both copies of the gene are lost or mutated the cell is transformed to a cancer phenotype. Examples are the proteins P53, retinoblastoma (Rb) and Wilm's tumour.


The cloudiness of a solution; the amount of solid particles that are suspended in water and that cause light rays shining through the water to scatter. Turbidity makes the solution cloudy or even opaque in extreme cases. Turbidity is measured by a nephelometer in which the cloudiness or turbidity is based on the amount of light that is reflected off particles in the water.  Turbidity is expressed in nephelometric turbidity units (NTU).


A device with a rotor turned by a moving fluid, such as water, steam, gas, or wind.A turbine changes kinetic energy (energy of movement) into mechanical energy (energy in the form of mechanical power).


Firm. Cells with walls become turgid as a result of the entry of water from a hypotonic environment.

Turgor pressure

The force directed against a cell wall after the influx of water and the swelling of a walled cell due to osmosis.

Turner syndrome

Occurs in females when one of the X (female) chromosomes is missing or damaged.
A genetic condition affecting girls with an incidence of 1 in 2500 female births. The most common features of Turner syndrome are short stature and reduced or absent development of the ovaries. As adults, women with this disorder are typically infertile.

Twin spot

A pair of mutant sectors within wild-type tissue, produced by a mitotic crossover in an individual of appropriate heterozygous genotype.

Twitch (muscle twitch)

A single brief muscle contraction of a muscle in response to a single stimulus that is at or above threshold.

Two-strand double crossover

A double crossover that involves only two of the four chromatids of a tetrad.


A plot from measurement of the ease with which sound flows through the eardrum membrane while air pressure against the eardrum is varied. It measures the movement of the eardrum, and can assist in determining if there is any factor impeding this movement form the normal pattern, such as fluid or pressure is present in the middle ear or a tear/hole in the eardrum, etc..

Typological thinking

The concept that organisms of a species conform to a specific norm.
In this view variation is considered abnormal.

Tyrosine kinase

An enzyme that catalyzes the transfer of phosphate groups from ATP to the amino acid tyrosine in a substrate protein. Tyrosine kinase can produce a diversity of cellular end effects, including effects exerted by 2nd messengers.  It is generally involved in long-term cellular changes such as occur in the process of development of an organism.

Tyrosine kinase receptors

A receptor protein in the plasma membrane that responds to the binding of a signal molecule by catalyzing the transfer of phosphate groups from ATP to tyrosines on the cytoplasmic side of the receptor.Binding of the transmitter to the binding site results in activation of tyrosine kinase.  The phosphorylated tyrosines activate other signal-transduction proteins within the cell.