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F1 (first filial generation)

The first filial or hybrid offspring in a genetic cross-fertilization.

F2 (second filial generation)

Offspring resulting from interbreeding of the hybrid F1 generation.

Face validity

The extent to which the items of a test or procedure appear at least superficially (i.e., at face value) to sample that which is to be measured. A property of a test intended to measure something. The test is said to have face validity if it "looks like" it is going to measure what it is supposed to measure. For instance, if you prepare a test to measure whether students can perform multiplication and everyone you show it to agrees that it looks like a good test of multiplication ability, you have shown the face validity of your test. In face validity, you look at the operationalization (the translation of a concept or construct into a functioning and operating reality) and see whether "on its face" it seems like a good translation of the construct.

Facilitated diffusion

The spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients. Particles move across the membrane down their electrochemical gradient, but are assisted to do so by transmembrane proteins.


One of two or more expressions that are multiplied together.

Factor analysis

Multivariate statistical analysis method. There are several variables X; can certain X terms be combined to give a higher dimension


The product of all the integers from 1 up to the integer in question. The (!) exclaimation point is used to mean factorial.

Factor theorem

If P(x) is a polynomial, then if P(r) = 0, then (x - r) is a factor of P(x).


Bacteria that can grow either with or without free oxygen present.

Facultative anaerobe

An organism that makes ATP by aerobic respiration if oxygen is present but that switches to fermentation under anaerobic conditions.

Facultative heterochromatin

Heterochromatin located in positions that are composed of euchromatin in other individuals of the same species, or even in the other homologue of a chromosome pair.

Fading (in learning)

The gradual removal of discriminative stimuli such as cues and prompts. A technique used to teach children appropriate behaviors or skills.

Failure to thrive (FTT)

A chronic disorder of infancy and childhood characterized
by growth failure, malnutrition and variable degrees of the delay in motor and social development.  Possible causes of FTT are varied; illness, oral-motor feeding and swallowing disorders, inadequate food resources and problems with parent-child interaction.

False-negative and False-positive

False-negative = A test result that shows no evidence of the disease or abnormality being investigated although the condition is actually present.
False-positive = A test result that shows evidence of a disease or an abnormal condition although it (the condition being tested for) is not present.

Familial dwarfism

An inherited form of dwarfism or arrested growth that results in overall smallness.

Familial Short Stature

A normal growth pattern that matches closely to the child’s family members. The bone age usually matches the child’s age.

Family (in genetics)

A category in the biological classification of plants and animals coming below an order and above a genus.

Fanconi Anemia

A rare inherited blood disorder that may lead to bone marrow failure.
Children with Fanconi Anemia are at higher risk for having birth defects, kidney problems, growth problems, and cancer.


Bundle of muscle cells (muscle fibers) See Muscle structure.


A small local contraction of muscles visible through the skin; represents spontaneous discharge in one or more muscle fibers innervated by a motoneuron.

Fascicular arrangement or Muscle Fiber Configurations 

The arrangements of the muscle fibers that make up a muscle give the muscle its characteristic appearance.
The arrangement of fascicles determines range and power;
example: parallel muscle - longer fascicles produce greater range of movement;
example: multipennate muscle - more fascicles produce more power
Muscles are described by the directions of the fibers compared to the long axis of the muscle, or the direction of the action it produces: 
Parallel - all muscle fibers are parallel to the long axis of the muscle. Because all the fibers go in the same direction and are parallel, when these muscles contract, they allow a greater movement of the insertion point.
Convergent - In these muscles the origin is wider than the insertion. The direction of the fibers is toward the middle of the muscle, which narrows toward the insertion. When these muscles contract they concentrate a greater force on the insertion.
Divergent - In these muscles the insertion is wider than the origin. The direction of the fibers is away from the center of the muscle. The contraction of these muscles allows for the greatest range of motion.
Circular - In these muscles, the fibers go around in circles. They function to seal off bodily openings, and contract with a great deal of force. 
Pennate muscle - Fascicle forms an oblique angle to the tendon (like a feather).
Unipennate muscle - short pennate fascicles run down one side of the tendon.
Bipennate muscle - short pennate fascicles run down both sides of the tendon.
Multipennate - muscle where the tendon branches within the muscle and short pennate fascicles are attached to each tendon branch.

Fast Fourier Transform (FFT)

An mathematical technique (algorithm) to convert a set of uniformly spaced points from the time domain to the frequency domain.
Used in acoustics to describe the frequency composition of a sound wave – e.g., in a complex sound, what are the simple sine wave components.  Similar applications are made in other areas of science and engineering, to convert a complex wave into its simple sine wave components.
Because of the transform from the time to the frequency domain, time information is lost – e.g., which frequencies in a complex signal occurred at what instants of time.  Hence, often wavelet analyses are preferred as they retain time domain information

Fasting glucose test

A blood test done to determine the plasma glucose concentration in the fasting state (the person has not eaten for 8 to 12 hours).  A fasting plasma concentration > 140 mg/dl on at least two occasions is diagnostic for diabetes mellitus.

Fast twitch and slow twitch muscle fibres

Muscle fibres differentiated on the basis of their energy metabolism and velocity of contraction
Slow twitch fibres or type I fibres depend on oxidative (aerobic) metabolism, and have a slower velocity of contraction.
Fast twitch fibres or Type II fibres, with a faster velocity of contraction, are differentiated into type IIA (which also depend on oxidative metabolism) and type IIB (which depend on glycolytic metabolism). The former is found in some mammals but is not abundant in humans.
Oxidative (aerobic) metabolism, which produces large amounts of ATP, is dependent on the availability of oxygen while glycolytic metabolism, which uses the breakdown of glucose to produce ATP, is limited by the glycogen stores in the muscle fibre but is independent of the availability of oxygen.
The velocity of contraction depends on the rate of hydrolysis of ATP by the myosin molecule and this depends on the myosin isoform present.
Fast twitch fibres are employed for short, intense bursts of contraction while slow twitch fibres predominate in muscles that are continuously active. Most skeletal muscles are a mixture of fast and slow twitch fibres.

Fat (Triacylglycerol)

A biological compound consisting of three fatty acids linked to one glycerol molecule.

Fate map

A map of an embryo showing areas that are destined to develop into specific adult tissues and organs.  A map of the developmental fate of a zygote or early embryo showing the adult organs that will develop from material at a given position on the zygote or early embryo.

Fat mass

Tissue of reserve energy for the body made up of all the cells of the fatty tissue.

Fatty acid

A long carbon chain carboxylic acid. Fatty acids vary in length and in the number and location of double bonds; three fatty acids linked to a glycerol molecule form fat.
Most common form of lipids found in all cells. Come in saturated (reduced) and unsaturated (oxidized) form and are a component of phospholipids and fats


A protein motif of approximately 50 amino acids that functions as a site of protein-protein interaction. F-box proteins were first characterized as components of SCF ubiquitin-ligase complexes (named after their main components, Skp I, Cullin, and an F-box protein), in which they bind substrates for ubiquitin-mediated proteolysis. The F-box motif links the F-box protein to other components of the SCF complex by binding the core SCF component Skp I. F-box proteins have more recently been discovered to function in non-SCF protein complexes in a variety of cellular functions. There are 11 F-box proteins in budding yeast, 326 predicted in Caenorhabditis elegans, 22 in Drosophila, and at least 38 in humans. F-box proteins often include additional carboxy-terminal motifs capable of protein-protein interaction; the most common secondary motifs in yeast and human F-box proteins are WD repeats and leucine-rich repeats, both of which have been found to bind phosphorylated substrates to the SCF complex. The majority of F-box proteins have other associated motifs, and the functions of most of these proteins have not yet been defined.

F Distribution

The F distribution is a family of distributions, one for each pair of degrees of freedom from an F test ratio. The distributions are generally asymmetrical and skewed to the right when the two degrees of freedom are low. The distributions become more symmetrical as the two degrees of freedom increase.

Febrile seizure

A seizure caused by a rapidly rising fever.  Febrile seizures are brief, and do not necessarily indicate that a child has epilepsy.

Fecal coliform

The part of the coliform bacteria that is present in the intestinal tracts and faeces of warm-blooded animals. A common pollutant in water.


Rate at which females produce offspring.

Feedback (in electronic devices)

The squeal from a hearing aid receiver that is produced when amplified sound from the receiver is picked up by the microphone and reamplified.

Feedback inhibition

A method of metabolic control in which the end-product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.

Feedback systems

Control mechanisms whereby an increase or decrease in the level of a particular factor inhibits or stimulates the production, utilization, or release of that factor; important in the regulation of enzyme and hormone levels, ion concentrations, temperature, and many other factors.

Feeder layer

Cells used in co-culture to maintain pluripotent stem cells.  For human embryonic stem cell culture, typical feeder layers include mouse embryonic fibroblasts (MEFs) or human embryonic fibroblasts that have been treated to prevent them from dividing.


A catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end-product, such as ethyl alcohol or lactic acid. A process of growing microorganisms to produce various chemical or pharmaceutical compounds. Microbes are usually incubated under specific conditions in large tanks called fermenters. Fermentation is a specific type of bioprocessing.


Capable of reproduction

Fertility factor (F factor)

The plasmid that allows a prokaryote to conjugate with and pass DNA into an F- cell.
A bacterial episome whose presence confers donor ability (maleness).
F' (F-prime) factor = A fertility factor into which a portion of the bacterial chromosome has been incorporated.
F+ (plus) cell = In Escherichia coli, a cell having a free fertility factor; a male cell.
F- (minus) cell = In Escherichia coli, a cell having no fertility factor; a female cell.
F-duction (also sexduction) = Sexual transmission of donor Escherichia coli chromosomal genes on the fertility factor. A process whereby a bacterium gains access to and incorporates foreign DNA brought in by a modified F factor during conjugation.
F-pili (also Sex pili) = Hair-like projections on an F+, an F' or Hfr bacterium involved in anchorage during conjugation and presumably through which DNA passes.


The process by which an egg is made capable of generating offspring. The union of haploid gametes to produce a diploid zygote. It is often synonymous with syngamy.

Fetal alcohol syndrome (FAS)

A pattern of physical and mental birth defects that are the direct result of a mother drinking alcohol while pregnant. Clinical features include prenatal and postnatal growth deficiency, CNS dysfunction, a particular pattern of facial characteristics and major organ system malformations.

Fetal programming

The concept that an adverse environmental stimulus experienced in utero during the critical period of organ formation (organogenesis) can induce long-term effects on the organism which may be manifested post-partum even in adulthood.
It is believed the adverse stimulus causes structural and functional deficits that will predispose the offspring to several diseases in adulthood, including hypertension and cardiovascular diseases.  This is especially so if the offspring has a low birth weight (often used as a marker of intrauterine stress) which has been correlated with chronic kidney disease, impaired renal sodium excretion, and increased susceptibility to cardiovascular disease and hypertension.


A procedure for examining the unborn baby using a needlelike camera, which is inserted into the womb to videoscan the fetus for visible abnormalities.


An unborn or unhatched vertebrate that has passed through the earliest developmental stages; a developing human from about the second month of gestation until birth.

F factor

A fertility factor in bacteria, a DNA segment that confers the ability to form pili for conjugation and associated functions required for the transfer of DNA from donor to recipient. May exist as a plasmid or integrated into the bacterial chromosome.

Fibonacci number (or Fibonacci sequence)

A member of the sequence of numbers such that each number is the sum of the preceding two. The first fourteen numbers are 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377....  
F(n) ≈ round(Φn/√ 5), where Φ=(1+√ 5)/2.

Fibrates (Fibric acid derivates)

Fibrates lower blood triglyceride levels by inhibiting production in
the liver of VLDL and speeding up the removal of triglycerides from the blood.


Any minute, threadlike structure within a cell.


The activated form of the blood-clotting protein fibrinogen, which aggregates into threads that form the fabric of the clot.


A term applied to a cell of a loose connective tissue that is separated from similar cells by some degree of matrix material. Fibroblasts secrete elastin and collagen protein, the protein ingredients of the extracellular fibers.


Formation or development of excess fibrous connective tissue in an organ as a result of a reparative or reactive process

Fibrous protein

Insoluble structural protein in which the polypeptide chain is coiled along one dimension.Fibrous proteins constitute the main structural elements of many animal tissues.


A region in space that is defined by a vector function. Common fields are: gravitational, electric and magnetic.

Field of vision

Refers to the breadth or degree of angle that a person can see without turning his or her head or moving the eyes: includes the limits of peripheral sight or that which lies to the sides of straight ahead.

Field potentials

Electrical activity from a large number of active neurones in the brain, recorded by an electrode placed within the brain. Currents caused by the mass activity of cells in a certain region can be recorded by an electrode inserted in the brain. Field potentials are dominated by the activity of the neurons bringing information into the cortical area in which the electrode is placed; thus the field potential is useful in identifying the input to that area. (see EEG)

Figure-ground discrimination

The process of distinguishing an object from its background. This occurs in all sensory systems, including vision, hearing, touch.


Long chain of proteins, such as found in hair, muscle, or in flagella. May refer to the appearance of an organism, a part of an organism, or a strand of cytoplasm.


A physical unit of storage on a computer disk or tape.

Filose pseudopodium (Plural = Filose pseudopodia)

Pseudopodia that are thin and threadlike but without internal skeletal elements.


A device used to allow the selective entry of particular substances while attenutating the entry of others e.g., Optical filters attenuate particular wavelengths of light while passing others; Sound filters attenuate particular frequencies of sound or while passing others; Filters for particle matter allow only particles of a certain size or less to go through but not larger particles.

Filter enrichment

A technique for recovering auxotrophic mutants in filamentous fungi (in which non-auxotrophic organisms are filtered off leaving a residue of non-growing auxotrophs).

Filter Forward Scatter (FSC) (in flow cytometry)

A parameter measuring light scattered less than 10 degrees as a cell passes through the laser beam. The FSC measurement is related to cell size


Fluid extracted by the excretory system from the blood or body cavity. The excretory system produces urine from the filtrate after extracting valuable solutes from it and concentrating it.


The first stage of kidney function. Blood plasma is forced, under pressure, out of the glomerular capillaries into Bowman's capsule, through which it enters the renal tubule.

Fimbriae (singular = fimbria)

Short, hair-like projections or appendages on the outer surface of certain bacteria composed of protein subunits (pilin) extending outward from the surface that act as a virulence factor by promoting adherence; formerly known as pili.


The characteristic spot pattern produced by electrophoresis of the polypeptide fragments obtained through denaturation of a particular protein with a proteolytic enzyme.

Finger spelling

Use of a manual alphabet (26 handshapes and positions that represent the 26 letters of the written alphabet) to spell words.  A form of sign language commonly used in both ASL and Signed English systems, for proper names and other terms for which there are no generally accepted signs.

First division segregation (FDS)

The allele arrangement (4+4) of spores within an ordered ascus that indicates the lack of recombination between a locus and its centromere. A linear pattern (4+4) of spore phenotypes within an ordered ascus for a particular allele pair, produced when the alleles go into separate nuclei at the first meiotic division, showing that no crossover has occurred between that allele pair and the centromere.

First law of thermodynamics

In all processes, the total energy of the universe remains constant.
The principle of conservation of energy. Energy can be transferred and transformed, but it cannot be created or destroyed.

First-pass metabolism

Drugs which are absorbed from the gut travel directly to the liver where some are extensively metabolised before they can reach their intended site of action.


1. Asexual reproduction in which the parent organism divides into two or more parts, each developing into genetically identical individuals.
2. Splitting the nucleus of an atom into smaller units.
Division of single-celled organisms, especially prokaryotes, in which mitosis does not occur. Also used to refer to mitosis in certain unicellular fungi.

Fit Probability

The fit probability (Fit Prob) is the probability that the computed standard points on the logistic curve are not significantly different from the observed points.The fit probability is derived from the residual variance.

Fitness (W)

The relative reproductive success of a genotype as measured by survival; fecundity or other life history parameters; The expected contribution of an allele, genotype, or phenotype to future generations
The fitness of genes and organisms is always relative to the other genes and organisms that are present in the same population. Usually it is measured as the average number of offspring produced by individuals with a certain genotype, relative to the number produced by other genotypes.
See Darwinian fitness.


To hold in place. Orthopedic hardware can be used to fixate bone, for example with fracture repairs. Bone can be used to fixate orthopedic hardware as with joint prostheses.

Fixed action pattern

A highly stereotypical behavior that is innate and must be carried to completion once initiated.

Fixed allele

An allele for which all members of the population under study are homozygous, so that no other alleles for this locus exist in the population.

Fixed breakage point

According to the heteroduplex DNA recombination model, the point from which unwinding of the DNA double helices begins, as a prelude to formation of heteroduplex DNA

Fixed format file

A file structure consisting of physical records of a constant size within which the precise location of each variable is based on the column location and width of the variable. Most data from ICPSR is distributed in a fixed format and codebooks are used to specify the column location and width of each variable. (See Free format file)


Lacking normal muscle tone; limp.

Flagged parameter

A flagged parameter is a parameter that is outside of a specified probability limit. A flagged parameter indicates a possible problem with one or more components in the test method.

Flagella (singular = flagellum)

Long, whip-like organelles used for locomotion in both prokaryotic and eukaryotic cells.; Hair-like structure attached to a cell, used for locomotion in many protists and prokaryotes.   The prokaryotic flagellum differs from the eukaryotic flagellum in that the prokaryotic flagellum is a solid unit made of helically-coiled protein subunits composed primarily of the protein flagellin, while the eukaryotic flagellum is composed of several protein strands bound by a membrane, and does not contain flagellinEukaryotic flagella have an internal arrangement of microtubules in a 9 + 2 array (nine outer doublet microtubules and two inner single microtubules, ensheathed in an extension of plasma membrane). These organelles are anchored in the cell membranes. The eukaryotic flagellum is sometimes referred to as an undulipodium.


A kind of protist bearing flagella; a very diverse group with unclear boundaries. distinguished from ciliates because flagella are few in number, and usually create a thrust along the length of the organelle rather than parallel to the body surface.

Flammable liquid

A liquid having a flash point below 100 degrees; more ignitable than combustible liquids.

Flanking region (of DNA)

The DNA sequences extending on either side of a specific locus or gene.

Flask or bottle cells

Epithelial cells found at the initial site of gastrulation, lining the initial archenteron, that temporarily become bottle-shaped. They maintain contact with the outer surface of the embryo, but the majority of the cell is inside the embryo.

Flash point

The lowest temperature at which a liquid gives off enough vapor to form an ignitable mixture and will burn when a source of ignition is present.

Flatmounting (of cortex)

A technique for preparing brains for anatomical analysis.
The cortex of the brain has a unique topology - it is a single sheet of tissues. However, it is heavily folded, which makes it difficult to observe large-scale structures on the cortex. Flatmounting is the technique of manually unfolding the complicated cortical surface to produce a single, flat sheet of cortex. It is now possible to use computer software to achieve the same effect virtually.


A group of molecules with a unique ring structure.  Flavin mononucleotide and Flavin dinucleotide (FMN and FAD) are part of the flavin group of molecules.

Flavin adenine dinucelotide (FAD)

A coenzyme that functions as an electron acceptor in the Krebs cycle


A constituent of Ginkgo biloba extract that has been found to reduce the level of free radicals by decreasing cell membrane lipid peroxidation.


Type of flavonoid found in citrus fruits. May provide the health benefits of neutralizing free radicals and possibly reducing the risk of cancer.

Flavor-profile method

The flavor-profile method consists of a small laboratory panel of 6 or 8 people trained in the method measure of the flavor profile of food products. Descriptive words and numbers, with identifiable meaning to each panel member, are used to show the relative strength of each note on suitable scale.


Decreasing the angle between articulating bones; bending a joint. For example, "Plantar Flexion" is the bending of the toes (or fingers) downwards towards the sole (or palm) while “Dorsi-flexion” is the bending of the toes (or fingers) upwards away from the sole (or palm).
Hence Flexor: A muscle that causes a limb or other body-part to bend.(see Extension)

Flight of ideas

A nearly continuous flow of accelerated speech with abrupt changes from topic to topic, usually based on understandable associations, distracting stimuli or plays on words. When severe, speech may be disorganized and incoherent. Flight of ideas is most frequently seen in manic episodes, but may also be observed in some cases of organic mental disorders, schizophrenia or other psychotic disorders and, occasionally, acute reactions to stress.


An overflow of water onto lands that are used or usable by man and not normally covered by water. Floods have two essential characteristics: The inundation of land is temporary; and the land is adjacent to and inundated by overflow from a river, stream, lake, or ocean.

Flood 100 year

A 100-year flood does not refer to a flood that occurs once every 100 years, but to a flood level with a 1 percent chance of being equaled or exceeded in any given year.

Flood plain

a strip of relatively flat and normally dry land alongside a stream, river, or lake that is covered by water during a flood.

Flood stage

The elevation at which overflow of the natural banks of a stream or body of water begins in the reach or area in which the elevation is measured.

Flow cytometry

Automated analysis of cells or subcellular components by detection of the fluorescence or light-scatter of sample fractions passing in narrow-stream droplets through a laser beam. Analysis of biological material by detection of the light-absorbing or fluorescing properties of cells or subcellular fractions (i.e., chromosomes) passing in a narrow stream through a laser beam. An absorbance or fluorescence profile of the sample is produced. Automated sorting devices, used to fractionate samples, sort successive droplets of the analyzed stream into different fractions depending on the fluorescence emitted by each droplet.

Flow karyotyping

Use of flow cytometry to analyze and/or separate chromosomes on the basis of their DNA content.

Flowing well/spring

a well or spring that taps ground water under pressure so that water rises without pumping. If the water rises above the surface, it is known as a flowing well.

Fluctuation test

A test used in microbial genetics to establish the random nature of mutation, or to measure mutation rates. An experiment by Luria and Delbruck that compared the variance in number of mutations among small cultures with subsamples of a large culture to determine the mechanism of inherited change in bacteria.

Fluency disabilities

Speech problems where the natural flow and rhythm of speaking is excessively interrupted, often by frequent pauses, prolongation of sounds, repetitions, or unrelated sounds.

Fluid mosaic model

The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids. The fluid mosaic model of cell membranes describes the structural and dynamical organization of biological membranes. It is composed of phospholipids that form large planar bilayers. In-between phospholipids exist membrane proteins and the alternating composition of phospholipids and proteins found in membranes has been compared to a mosaic structure. In addition, both components are not fixed in space but can freely move within the plane of the membrane. This 'fluidity' similar to the fluid or liquid state of water if it is nor frozen is essential for the proper function of proteins in membranes.


A dye used for tracing neuronal pathways after injection into the vicinity of neurons.
It is injected into the brain in a small amount and travels backwards (from neuronal terminals to cell bodies (i.e., it is a retrograde tracer).


Fluorescence immunoassays (FIA) are competitive binding immunoassays in which the analyte content of the sample is measured by the amount of fluorescence from bound labeled ligand. FIAs can also use a fluorogenic enzyme to tag the tracer and measure the formation of a fluorescent product.


Molecules that produce a fluorescent emission when irradiated with light at a suitable excitation wavelength. See Fluorescence


A molecule that emits light at certain wavelengths; often used to tag antibodies or other proteins and nucleic acids.


Emission of light by excited molecules as they revert to the ground state.
Fluorescence is the property of certain molecules, or fluorophores, to absorb light at one wavelength and emit a light at a longer wavelength. The incident light excites the molecule to a higher level of vibrational energy. As the molecule returns to the ground state, the excited fluorophore emits a photon. This photon is the fluorescence emission. If the molecule returns to the ground state through an intermediate excited triple state, there is a delay in the emission of the photon. This delayed photon is termed a phosphorescence emission.

Fluorescence In Situ Hybridization (FISH)

A technique that employs fluorescent molecular tags to detect probes hybridized to chromosomes or chromatin; useful for genetic mapping and detecting chromosomal abnormalities. A physical mapping approach that uses fluorescein tags to detect hybridization of probes with metaphase chromosomes and with the less-condensed somatic interphase chromatin.

Fluorescence Polarization Immunoassay

Fluorescence polarization immunoassays (FPIA) are homogenous competitive binding immunoassays in which fluorophore-labeled ligand competes with the unlabeled ligand for binding sites on the specific binder. When excited with polarized light, fluorophore ligands bound to binder rotate more slowly and emit light at a higher intensity than do free labeled ligands.

Fluorescent Label

A fluorescent label is either a fluorescent molecule, or an enzyme system that generates a fluorescent product, which is linked to a ligand or binder tracer.
The tracer is quantified by measuring the amount of light emitted by the tracer at a specific wavelength after exciting the tracer with incident light of a shorter wavelength. Fluorescent molecules include fluorescein and lanthanide chelates such as europium, samarium, and terbium.


A radiologic technique in which a fluoroscope is used to visually examine the body or an organ. A fluoroscope utilizes an X-ray tube and fluorescent screen, with the area to be viewed placed between the screen and the tube. This immediate imaging, when coupled with an image intensifier, is invaluable in situations such as cardiac catheterization, thin needle biopsies of tumors, and localization of foreign bodies.

Focal motor seizure

Seizures that affect specific motor, sensory, and psychomotor functions and originates from a particular area of the brain that governs or controls various motor functions. Focal seizures usually show themselves as a jerking in a single limb or one side of the body.


Point at which converging rays meet and at which a clearly defined image can be obtained.

Fokker-Planck equation

An equation that describes diffusion processes. It is used by population geneticists to describe random genetic drift.

Foley Catheter

This is a tube inserted into the urinary bladder for drainage of urine.
The urine drains through the tube and collects into a plastic bag.

Follicles (ovary)  

Structures in the ovary consisting of a developing egg surrounded by a layer of follicle cells. A microscopic structure in the ovary that contains the developing ovum and secretes estrogens.

Follicle stimulating hormone (FSH)

A gonadotropin (hormone from the pituitary gland) that stimulates the ovaries to produce eggs or the testes to produce sperm.


Inanimate object capable of transmitting infectious organisms to a host, e.g., soiled clothes, tissues and handkerchiefs, food processing equipment, dishrags, etc.


Soft membranous areas in the human cranial bones.The fontanelles do not ossify (form bony structures) until the child is 14 to 18 months old


All implantable orthopedic hardware in the United States must be approved by the Food and Drug Administration (FDA). The FDA classification of hardware is specified in the code of federal regulations (CFR) under Title 21, part 888, Orthopedic Devices. Devices are classified by type and anatomic region. For joint replacements, the main classification areas are the degree of constraint, composition, cemented or noncemented., and a few subcategories. The classification can be found by searching the Center for Devices and Radiological Health Database at http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm.

Foot and Mouth disease

The disease is caused by a virus and is highly contagious but not dangerous to man. Clinical signs are essentially similar in all species although the severity may vary considerably. The principal signs are pyrexia followed by vesicle formation in the mouth and feet resulting in salivation and lameness.
All species of cloven-hoofed animals are susceptible to FMD, including domestic livestock and wild ungulates such as buffalo, antelope and warthogs.


A technique to determine the length of nucleic acid in contact with a protein, or to identify a protein binding site on cellular DNA In the first definition: While in contact the free DNA is digested. The remaining DNA is then isolated and characterized.
In the second case: The presence of a bound protein prevents DNase from "nicking" that region, which can be detected by an appropriately designed gel.


An action (transfer of energy) that will accelerate a body in the direction of the applied force.

Forced vital capacity (FVC)

The maximum volume of gas that can be exhaled over a specific time period

Formatted Raw Data

The formatted raw data are the sample response data obtained directly from an instrument and processed into a standardized format.

Form constancy

The ability to recognize an object or shape, regardless of what position or angle it is viewed from.

Form errors

Common language errors made by children with language problems in which they have difficulty understanding or using the rules of grammar.  A child with this problem might say "We go pool" instead of "We went to the pool".

Formula unit

The simplest whole-number ratio which will describe an ionic crystal lattice.


Addition of nutrients not naturally present in the food or addition of amounts greater than those naturally present. Differs from "enrichment," which refers to the addition of nutrients to replace those lost in food processing. Important examples of food fortification include the addition of iodine to salt, the addition of vitamin D to milk, and the addition of the B vitamin folic acid to grain products.

Forward mutation

A mutation that converts a wild-type allele to a mutant allele.

Founder effect

The loss of genetic diversity when a new colony is formed (e.g. on an oceanic island) by a very small number of individuals from a larger population elsewhere.


A small area in the center of the retina in which the photoreceptor type known as cones are concentrated.The fovea is the region of colour vision and other properties associated with the cones and of greatest acuity, a property associated with the way information converges from photoreceptors to the nerve fibres, the retinal ganglion cells.


A nested pattern that shows the same symmetry/geometry at any scale a pattern is looked at. It is an example of an infinite pattern in both larger and smaller dimensions. Fractals are geometrical abstractions and sometimes used to explain complexity in living organisms, also the comparison does not hold up on closer inspection. As abstractions, they are thought to continue into infinity, even the infinitely small, although physicists believe that there is a material limit to the what constitutes the smallest dimension. As for complex biological organisms, their structure is hierarchical with higher levels having emergent structures and properties not found at the lower levels. Thus it is not a true fractal.


Controlled crystallization and separation techniques involving the separation of hard and soft fractions of a substance. Such processes are often employed in the production of oils, high stability frying oils and cocoa butter alternatives fats.


A break in bone or cartilage. Although usually the result of trauma, a fracture can be caused by an acquired disease of bone such as osteoporosis or by abnormal formation of bone in a disease such as osteogenesis imperfecta ("brittle bone disease"). Fractures are classified according to their character and location as, for example, a greenstick fracture of the radius.

Fragile site

A chromosomal region that has a tendency to break.

Fragile X syndrome

Chromosomal abnormality of the X chromosome; results from a mutation in a gene, the Fragile X Mental Retardation 1 (FMR1) gene, on the X chromosome.
A hereditary mental disorder, partially explained by genomic imprinting and the addition of nucleotides to a triplet repeat near the end of an X chromosome.
Full mutation of the gene means that cells do not produce a protein involved with communications between neurons in the central nervous system. The resulting disorder, Fragile X syndrome (FXS), occurs in approximately one in 2,500 births. It is associated with two other condtions, fragile X-associated tremor/ataxia syndrome and fragile X-associated primary ovarian insufficiency, also resulting from variations in the same gene even though they have different symptoms.
People with FXS often have intellectual disabilities ranging from mild to severe. They may also have emotional and behavioral problems, including attention problems, hyperactivity, anxiety, aggression, enlarged testes, rambling perseverative speech and autism or autism spectrum disorder.
People with a less dramatic change in the gene have what is called a pre-mutation, which increases their chance of having a child with FXS. These people may not have any apparent health problems or may have symptoms of Fragile X-associated Tremor/Ataxia syndrome or Fragile X-Associated Primary Ovarian Insufficiency, conditions associated with fragile X syndrome. Fragile X-associated Tremor/Ataxia syndrome (FXTAS) occurs primarily in older men. The principal symptoms are tremor and gait problems, but the condition also includes cognitive decline, anxiety, and depression. Fragile X-associated Primary Ovarian Insufficiency (FXPOI) occurs in women of childbearing age. Women with FXPOI may experience early infertility and increased risk of osteoporosis and heart disease.


A mutation in which there is an addition or deletion of one, two or a small number (not a multiple of three) of nucleotides that causes the codon reading frame to shift to one of two others from the point of the mutation during translation. Consequently the amino acid sequence of the protein is altered from the point of the mutation to the carboxy terminus.

Frameshift mutation

The insertion or deletion of a nucleotide pair or pairs, causing a disruption of the translational reading frame. A mutation occurring when the number of nucleotides inserted or deleted is not a multiple of 3, thus resulting in improper grouping into codons.

Free choice profiling (FCP)

Quantitative descriptive process, in which each panelist evaluates products using their own list of descriptors and scale. Training to coordinate the panel performance is not necessarily required. Evaluation is by multivariate statistical methods.

Free energy (G)

The component of the total energy of a system that can do work at constant temperature and pressure.A quantity of energy that interrelates entropy (S) and the system's total energy (H); symbolized by G. The change in free energy of a system is calculated by the equation G = ΔH – T ΔS, where T is absolute temperature.  The Free energy change (∆G) = The amount of free energy released (negative ∆G) or absorbed (positive ∆G) in a reaction at constant temperature and pressure.

Free energy of activation

Energy needed to initiate a chemical reaction.The initial investment of energy necessary to start a chemical reaction; also called activation energy.

Free-floating anxiety

Severe, generalized, persistent anxiety not specifically ascribed to a particular object or event and often a precursor of panic.

Free format file

A physical file structure that specifies the order of variables in a file and that they are delimited from each other by a special character or characters (usually a blank or other whitespace). Free format files may have variable physical record lengths ; when they do, they are typically delimited by a newline character (one or two bytes which denote the end of a line) at the end of each line. (See Fixed format file)

Free Fraction

The free fraction of an immunoassay reaction is the fraction of ligand which is not bound to the binder. When the free fraction is measured in isotopic tests, the average raw response of the (free) samples is subtracted from the raw response average of the tracer activity samples to yield the bound raw response. The bound raw response is then used to calculate the adjusted, normalized and y-axis responses

Free radicals

Atoms or molecules with an unpaired electron; A highly reactive molecule used to start the production of a polymer chain. Formation of free radicals is a normal oxidation process in foods and free radicals are formed during food treatments such as toasting, frying, freeze drying, and irradiation. They are generally very reactive, unstable structures that continuously react with substances to form stable products. Free radicals disappear by reacting with each other in the presence of liquids, such as saliva in the mouth. Consequently, their ingestion does not create any toxicological or other harmful effects.

Free testosterone

Testosterone in the body that is biologically active and unbound to other molecules in the body, such as sex hormone binding globulin.

Freeze fracture technique

A technique used to look at membranes that reveal the pattern of integral membrane proteins.

  1. Cells are quickly frozen in liquid nitrogen (196oC), which immobilizes cell components instantly.
  2. Block of frozen cells is fractured. This fracture is irregular and occures along lines of weakness like the plasma membrane or surfaces of organelles.
  3. Surface ice is removed by a vacuum (freeze etching).
  4. A thin layer of carbon is evaporated vertically onto the surface to produce a carbon replica.
  5. Surface is shadowed with a platinum vapor.
  6. Organic material is digested away by acid, leaving a replica.
  7. Carbon-metal replica is put on a grid and examined by a transmission electron microscope.

Freezing point

The temperature at which a liquid becomes a solid.  Increased pressure usually raises the freezing point.

Freezing point depression

Colligative property associated with the number of dissolved molecules. The lower the molecular weight, the greater the ability of a molecule to depress the freezing point for any given concentration. For example, in ice cream manufacturing, monosaccharides such as fructose or glucose produce a much softer ice cream than disaccharides such as sucrose, if the concentration of both is the same.

Frequency-dependent selection

A decline in the reproductive success of a morph resulting from the morph's phenotype becoming too common in a population; a cause of balanced polymorphism in populations.

Frequency Distribution

A frequency distribution is a systematic way to order a set of data from lowest to highest value showing the number of occurrences (frequency) at each value or range of values.

Frequency modulation

The system of audio transmission that uses a carrier wave and modulates its frequency to transmit sound. Used in radio broadcasting and in hearing aids and auditory trainers (FM systems) which relay sound through the FM waves in the air.


water that contains less than 1,000 milligrams per liter (mg/L) of dissolved solids; generally, more than 500 mg/L of dissolved solids is undesirable for drinking and many industrial uses.


The resistance that occurs when two objects rub together.
The interaction between surfaces: a measure of the resistance felt when sliding one body over another.

Friedrich’s ataxia (FRDA)

Reduction of the mitochondrial protein frataxin results in the accumulation of iron and reactive oxygen species, leading to oxidative damage, neurodegeneration and a reduced life span.

Frontal lobes

One of the four lobes of the brain; the front part of the brain.
Divided into motor, pre-motor and pre-frontal areas. The pre-frontal area is responsible for many cognitive functions such as planning, organizing, problem solving, selective attention, personality and a variety of "higher cognitive functions".

Frustration Tolerance

The ability to persist in completing a task despite apparent difficulty.
Individuals with a poor frustration tolerance will often refuse to complete tasks which are the least bit difficult. Angry behavior, such as yelling or throwing things while attempting a task is also indicative of poor frustration tolerance.


The mineral "skeleton" (siliceous lorica) of a diatom or other unicellular organism.

F test

An F test is a statistical test which computes the probability that the ratio of two variances from two different populations are equal.

FTP (File Transfer Protocl)

A reliable method of transferring files over the internet.

Functional alleles

Mutants that fail to complement each other in a cis-trans complementation test.

Functional antagonism

(or physiological antagonism). Reversal of the effects of a drug by an agent which, rather than acting at the same receptor, causes a response in the tissue or animal which opposes that induced by the drug. Examples include agents which have opposing effects on an intracellular second messenger, or, in an animal, on blood pressure. A functional antagonist can sometimes produce responses which closely mimic those of the pharmacological kind.

Functional articulation disorders

Refers to articulation problems that are not due to structural defects or neurological problems, but are more likely the result of environmental or psychological influences.

Functional genomics

Gaining clues to gene function by manipulation of genomic DNA.
Genomic DNA is usually manipulated with recombinant technologies (gene knockout or knockin) or by inhibition of gene expression with antisense oligonucleotides or small molecules.

Functional group

The specific atom or group of atoms that confers a particular chemical property on a biomolecule.

Functional residual capacity (FRC)

The volume of air remaining in the lungs after a normal exhalation

Fundamental number

The number of chromosome arms in a somatic cell of a particular species.

Fundamental particles

Those particles that are not known to contain any smaller components: leptonsquarks and gauge bosons.

Furchgott analysis

A method of measuring the affinity of an agonist by comparing its concentration-response curve before and after inactivating a proportion of the receptors with an irreversible antagonist. See Furchgott (1966) or Bowman and Rand (1980).


1.  Change of state of a substance from a solid to a liquid. 
2.  The joining together of two atomic nuclei.

Fusion gene

A hybrid gene created by joining portions of two different genes (to produce a new protein) or by joining a gene to a different promoter (to alter or regulate gene transcription).

Fusion protein (F protein)

A protein derived from the Sendai virus which can be used in the laboratory to cause cell fusion between somatic cells (any cell that is not a gamete).
It is also used to make fusogenic vesicles.