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Abbreviation for the real numbers.

Rachicentesis (also known as rachiocentesis)

Lumbar puncture for examination of the spinal fluid.

Rachio / Rachi

Pertaining to the spinal cord.
Rachiocampsis - Curvature of the spine.
Rachiochysis- Effusion of fluid within the vertebral canal.
Rachiokyphosis - Humpbacked curvature of spine; kyphosis.
Rachiomyelitis - Inflammation of the spinal cord.
Rachioparalysis - Paralysis of the spinal muscles.
Rachiopathy - Any disease of the spine.
Rachioplegia - Spinal paralysis.
Rachioscoliosis - Lateral curvature of the spine.
Rachiotomy - Incision into a vertebral canal for exploration.
Rachisagra - Pain or gout in the spine.
Rachischisis - Abnormal congenital opening of the vertebral column.
Rachitomy - Surgical or anatomic opening of the vertebral canal.

Radial cleavage

A type of embryonic development in deuterostomes in which the planes of cell division that transform the zygote into a ball of cells are either parallel or perpendicular to the polar axis, thereby aligning tiers of cells one above the other.

Radial symmetry

Characterizing a body shaped like a pie or barrel, with many equal parts radiating outward like the spokes of a wheel; present in cnidarians and echinoderms.


The ratio of an arc of a circle to the radius of the circle. On a unit circle, a full rotation around the circle is 2pi radians. On any circle, a full rotation is 2pi r radians.


1.  Transfer of heat between bodies without a change in the temperature of the intervening medium. 
2.  Any release of energy from its source, emitted in the form of waves or particles.
3. Event of rapid cladogenesis, believed to occur under conditions where a new feature permits a lineage to move into a new niche or new habitat, and is then called an adaptive radiation.

Radical (free radical)

Highly reactive atom or molecule containing one or more unpaired electrons.


Radioactivity is the emission of subatomic particles and radiation from elemental isotopes having unstable atomic nuclei. The isotopes used in radioimmunoassays emit either beta particles or gamma radiation. This radioactive decay is a random event and follows a poisson distribution.

Radioactive dating

A method of determining the age of fossils and rocks using half-lives of radioactive isotopes.

Radioactive isotope

An isotope, an atomic form of a chemical element, that is unstable; the nucleus decays spontaneously, giving off detectable particles and energy

Radioimmunoassay (RIA)

Radioimmunoassay (RIA) is a heterogeneous competitive binding immunoassay in which the tracer material is a radioactive isotope.

Radiometric dating

A method paleontologists use for determining the ages of rocks and fossils on a scale of absolute time, based on the half-life of radioactive isotopes


The distance from the center to a point on a circle.The line segment from the center to a point on a circle.


Gram-negative rods occurring in freshwater. They are occasionally isolated from human clinical specimens, but are not considered clinically significant.

Raman spectroscopy

A microscopy technique using laser beams to enable identification of materials used in construction of an object, those used in decorating the object’s surface, and can also be used to identify corrosion products, e.g. rust, on the surface of the object.
Raman spectroscopy works by shining a laser beam onto the object’s surface. Most of this light is reflected off unchanged. However a small proportion interacts with the molecules in the material and is scattered. The scattered portion of light, known as the Raman effect, is collected to produce a spectrum. Each material has a unique spectrum associated with it and therefore each one acts as a fingerprint with which to identify materials. However, the Raman effect is very small and until recently its use as an analytical tool was limited by a lack of suitable equipment. Recent advances, particularly the development of lasers, mean that Raman spectroscopy is now widely used to analyse a wide range of materials. These spectra can be used to identify a variety of materials from plastics to precious gemstones.
Raman spectroscopy is totally non-destructive and by using a microscope, spectra can be recorded from very small samples. Special attachments on the laser Raman microprobes even allow analysis of tiny areas directly on the surface of objects.
Source: British Museum)

Random error

Random error is the component of the total error which is due to chance alone.

Random genetic drift

Changes in allelic frequency due to sampling error. Changes in allele frequency that result because the genes appearing in offspring are not a perfectly representative sampling of the parental genes. (eg. in small populations).

Random primed synthesis

If you have a DNA clone and you want to produce radioactive copies of it, one way is to denature it (separate the strands), then hybridize to that template a mixture of all possible 6-mer oligonucleotides. Those oligos will act as primers for the synthesis of labeled strands by DNA polymerase (in the presence of radiolabeled precursors).


The set of all possible values for the output of a function.

Range of motion (ROM)

Refers to movement of a joint (important to prevent contractures).

Rank (in taxonomy)

In traditional taxonomy, taxa are ranked according to their level of inclusiveness.
Thus a genus contains one or more species, a family includes one or more genera, and so on.

Raster plots or diagrams

A drawing or representation of the time of occurrence of action potentials.
This is a representation of the occurrence of action potentials over some period of time that may include a stimulus. In this representation (on a computer screen generally) a dot or vertical line is drawn for each action potential fired by a neuron.  Each epoch of time from which recordings are obtained is displayed by a line on which the dots show the time at which APs occurred and blank spaces show that no APs occurred at that time). Successive recording epochs representing successive repetitions of the same stimulus or behavioural condition can then be displayed by shifting each line of dots and blank spaces vertically   so that the overall representation is of a series of horizontal lines of dots + blank spaces, as shown below:


Some of these species are phytopathogens of terrestial plants. Their main habitats are their respective plant hosts.

Rating curve

A drawn curve showing the relation between gage height and discharge of a stream at a given gaging station.


A ratio is a mathematical formula which divides a numerator by a denominator.
The ratio of two real numbers, and b, is a/b. Normalized responses, baseline monitor points, and screening test results are all examples of ratios.

Rational number

A number that can be expressed as the ratio of two integers.

Raw data

The raw data are the unprocessed sample response data which are transmitted directly from the detector instrument

<Raw Response

The raw response of a sample is the raw data of that sample, in the form which it is used for the computation of the assay run. The average of the instrument background raw response is subtracted from raw response of each sample before any computations are performed. The raw response, minus the background raw response, is stored in the appropriate test data and archive files.


A starting material in a chemical reaction; substances that take part in a chemical reaction.


When two or more chemicals combine to make a new chemical substance

Reaction rate

The amount of reactant converted to product in a set period of time.

Reactive arthritis

A chronic form of arthritis featuring the following three conditions: (1) inflamed joints; (2) inflammation of the eyes ( conjunctivitis ); and (3) inflammation of the genital , urinary or gastrointestinal system.

Reactive schizophrenia

A type of schizophrenia attributed primarily to strong predisposing and/or precipitating environmental factors; usually of rapid onset and brief duration, with the affected individual appearing well both before and after the schizophrenic episode.

Reading frame

The succession of codons determined by reading nucleotides in groups of three from a specific initiation codon. When mRNA is translated by the cell, the nucleotides are read three at a time. By starting at different positions, the groupings of three that are produced can be entirely different. The reading frame that is actually used is determined by the first methionine codon (the initiation codon). Once that first AUG is recognized, the pattern of triplet groupings follows unambiguously.


Transcription or translation beyond the normal termination signals in DNA or mRNA respectively.

Reagent Blank

A reagent blank is a baseline standard sample from a one standard screening test which measures the amount of nonspecific activity present in the reaction. The amount of nonspecific activity is measured by omitting the binder in labeled ligand (competitive binding) assays or the ligand in labeled binder (sandwich binding) assays.

Real numbers

The union of the set of rational numbers and irrational numbers.


The process of enlarging a cavity so that a prosthesis can be inserted. Reaming most commonly is performed in the femur for insertion of a femoral nail.


Spontaneous realignment of two single DNA strands to re-form a DNA double helix.


Mode of thinking
Abstract Reasoning = Mode of thinking in which the individual recognizes a phrase that has multiple meanings and selects the meaning most appropriate to a given situation. The term "abstract" typically refers to concepts not readily apparent from the physical attributes of an object or situation.

Concrete Reasoning = The ability to understand the literal meaning of a phrase.

Problem-Solving Reasoning = The ability to analyze information related to a given situation and generate appropriate response options. Problem-solving is a sequential process that typically proceeds as follows: identification of problem; generation of response options; evaluation of response option appropriateness; selection and testing of first option; analysis as to whether solution has been reached. A patient/client may discontinue making a cup of coffee because the sugar bowl is empty, even though sugar is readily available in a nearby cabinet. A patient/client may easily navigate his way into a room crowded with furniture, but request staff assistance to navigate his way out.

Sequencing Reasoning = The ability to organize information or objects according to specified rules, or the ability to arrange information or objects in a logical, progressive manner. Nearly every activity, including work and leisure tasks, requires sequencing. For example, in cooking certain foods it is important that ingredients be added and mixed in a specified order; in dressing, undergarments must be put on prior to outergarments.

Receptive aphasia

Impairment of receptive language due to a disorder of the central nervous system.

Receptive language disorders

Difficulties in comprehending what others say.


A structure (a specific protein molecule) on or within a cell where a drug or natural signalling molecule (e.g., hormone) acts to produce its effect.

Receptor-mediated endocytosis

The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.

Receptor potential

A change in the resting membrane potential of a specialized cell (receptor cell) that detects a stimulus, produced by the stimulus to which the receptor cell is specific.
The receptor potential is the biological response to a physical stimulus (e.g., light,sounds, chemicals, pressure, etc) and is themechanism whereby the body translates the physical stimulus into a biologically-recognisable form. The size of the receptor potential is proportional to the intensity of the stimulus; in turn the size of the receptor potential determines the number of Action Potentials produced by neurons receiving input from that receptor cell, and conveying the information on the presence and intensity of the physical stimulus, ultimately to the brain.

Receptor reserve

Because high-efficacy compounds need to occupy relatively few receptors to produce a maximal response, it is possible to inactivate a proportion of the receptors in a tissue (e.g. in the presence of an irreversible antagonist) without depressing the maximum of the concentration-response curve. (The curve is, however, shifted rightward along the x axis). There is said to be a receptor reserve (or, more colloquially, spare receptors) for that particular agonist in that particular tissue. There is no receptor reserve for a drug which acts as a partial agonist in the tissue. The receptor reserve may vary between tissues, depending on the number of receptors in the particular tissue and the efficiency of coupling between them and their effector mechanism. Consequently, a partial agonist in one tissue may appear to act as a full agonist in a tissue with a higher receptor reserve.

Red eye

Also called conjunctivitis. Redness or irritation of the conjunctivae, the membranes on the inner part of the eyelids and the membranes covering the whites of the eyes. These membranes react to a wide range of bacteria , viruses , allergy-provoking agents, irritants and toxic agents. Viral and bacterial forms of conjunctivitis are common in childhood.

Recessive (allele)

In a heterozygote, the allele that is completely masked in the phenotype.
An allele that is not expressed in the heterozygous condition; a character which was not evident in the first filial generation (F1) of a cross between two pure-breeding strains differing in respect of this character, and which re-appeared in one quarter of the second filial generation (F2).
The recessive character is expressed phenotypically in the homozygous or hemizygous state.
Hence recessive phenotype = The phenotype of a homozygote for the recessive allele; the parental phenotype that is not expressed in a heterozygote.


water added to an aquifer. For instance, rainfall that seeps into the ground.


The reciprocal of a number, a, is 1/a, (a cannot be zero).

Reciprocal altruism

Altruistic behavior between unrelated individuals; believed to produce some benefit to the altruistic individual in the future when the current beneficiary reciprocates.

Reciprocal translocation

A chromosomal configuration in which (usually) the ends of two non- homologous chromosomes have become exchanged.  A translocation in which part of one chromosome is exchanged with a part of a separate non-homologous chromosome.

Reclaimed wastewater

treated wastewater that can be used for beneficial purposes, such as irrigating certain plants.

Recognition site / sequence

A specific sequence of nucleotides at which a restriction enzyme cleaves a DNA molecule. A nucleotide sequence—composed typically of 4, 6, or 8 nucleotides--that is recognized by a restriction endonuclease.

Recognition species concept

The idea that specific mating adaptations become fixed in a population and form the basis of species identification.


In genetic mapping studies an offspring having a non-parental allele combination, i.e., an offspring whose phenotype differs from that of the parents. An individual or cell with a genotype produced by recombination.

Recombinant clones

Clones containing recombinant DNA molecules.

Recombinant DNA (rDNA)

A hybrid DNA formed in vitro from two or more different organisms.by joining together DNA fragments from different sources using recombinant DNA technologies Or The molecule formed by joining a DNA of interest to vector DNA.
New combinations of DNA fragments formed by cutting DNA segments from two sources with a restriction enzyme and then joining the fragments together with DNA ligase, or DNA fragments are linked to self-replicating forms of DNA to create recombinant DNA molecules. These molecules in turn are replicated in a host cell to create clones of the inserted segments. By extension, the adjective "recombinant" is applied to any molecule produced from an organism with modified DNA (e.g., recombinant vaccine).

Recombinant DNA technologies

Procedures used to join together DNA segments in a cell- free system (an environment outside a cell or organism). Under appropriate conditions, a recombinant DNA molecule can enter a cell and replicate there, either autonomously or after it has become integrated into a cellular chromosome.


The formation of new gene combinations; The process by which progeny derive a combination of genes different from that of either parent.  In eukaryotes, it may be accomplished by new associations of chromosomes produced during sexual reproduction or crossing over; in prokaryotes, may be accomplished through transformation, conjugation, or transduction.

Recombination occurs naturally in plants and animals during the production of sex cells (sperm, eggs, pollen) and their subsequent joining in fertilization. In microbes, genetic material is recombined naturally during conjugation.
In higher organisms, this can occur by crossing over between their loci during meiosis. Recombination may come about through random orientation of non-homologous chromosome pairs on the meiotic spindles, from crossing-over between homologous chromosomes, from gene conversion, or by other means.

Recombinational repair

The repair of a DNA lesion through a process, similar to recombination, that uses recombination enzymes.


The smallest recombinable unit within a cistron.  A region of a gene within which there can be no crossing-over; now known to be a single nucleotide pair.

Reconstruction nail

A femoral intramedullary nail used to fixate femoral neck, intertrochanteric, and subtrochanteric fractures. There is a proximal hold for an interlocking femoral screw that is placed in the femoral neck or head.

Record (in computing)

Depending on the context, "record" may refer to a physical record or a logical record.

Record length (in computing)

Depending on the context, the length in bytes (i.e., columns) of a physical record or a logical record. On ICPSR Tape Information Forms and on CDNet, the abbreviation "RecLen" is used for physical record length.

Record type (in computing)

A record that has a consistent logical structure. In files that include different units of analysis, for instance, different record types are needed to hold the different variables. For example, one record type might have a variable for income in one column and another record type might have a variable for household size in that same column. The codebook will describe these different structures and how to determine which is which so that you can tell your statistical software how to interpret that particular column as income or household size.

Recovery (in assays)

The recovery of an analyte is an analytical procedure which is used to measure the inaccuracy of the test method. Recovery is measured by assaying a sample after adding a known amount of the analyte and the same sample without added analyte.

Recreation Therapist

Individual within the facility responsible for developing a program to assist persons with disabilities plan and manage their leisure activities; may also schedule specific activities and coordinate the program with existing community resources.

Rectangular coordinates

Same as Cartesian Coordinates.

Rectifier ion channels

An ion channel through which ions flow more readily from one side of the membrane to the other than in the reverse. Ion channels are termed as ‘ohmic’ or ‘rectifier’ channels. In the first case the ion flow is directly proportional to the voltage (I = Vm/R). In the second case the flow is not linearly related to the voltage as the ions flow more readily in one direction than the other. (see Ion channels or Ohmic ion channels)

Recycled water

water that is used more than one time before it passes back into the natural hydrologic system.

Redox pair (Reduction-oxidation pair)

An electron donor and its corresponding oxidized form; for example, NADH and NAD+.

Redox reaction

A reaction in which electrons are transferred from a donor (the reducing agent) to an acceptor molecule (the oxidizing agent). Also called oxidation-reduction reaction.
Hence reducing agent = The electron donor in an oxidation-reduction reaction, and reduction = the gain of electrons by an ion or compound.

Reduction division

A nuclear division that produces daughter nuclei each having one-half as many centromeres as the parental nucleus. The first meiotic division reduces the number of chromosomes and centromeres to half that of the original cell.

Redundant / Repetitive DNA

DNA made up of copies of the same or nearly the same nucleotide sequence. DNA sequences that are present in many copies per chromosome set. Repetitive DNA sequences may be closely linked (eg satellite DNA or VNTR loci) or dispersed throughout the genome or parts of the genome (eg alu family).

Reference Assays

The reference assays are a fixed set of stable assays which are statistically compared to a single assay or multiple assays to detect changes in reagents or incubation conditions. These reference assays, by default, are the first 30 assays run on StatLIA for each test method.  With a reference set of at least two assays, standard curve and control specimen parameters in today's assay are statistically compared to the same parameter in the reference assays to identify any statistically significant differences.

Reference Range

The reference range of a subpopulation is an analyte concentration range encompassing a defined percentage of all of the members of that subpopulation.

Reference Curve

The reference curve is a single standard curve computed from the standard responses of all of the reference assays.

Reference Cutoff

A reference cutoff is an analyte concentration which divides the unknowns within a subpopulation into negative (those specimen concentrations less than the cutoff value) and positive (those specimen concentrations equal to or greater than the cutoff value).


Mirror image.


An automatic reaction to a stimulus, mediated by the spinal cord or lower brain.

Reflex activation

There are many sensor organs in the body that detect changes in things such as blood pressure or the composition of blood. These sensors send information to the brain to change the activity of nerves that control bodily functions. Physiological ‘reflexes’ can, therefore, be activated by changing blood pressure or the composition of the blood.

Reflexive property

xfor all x.  Every number equals itself.


The bending and slowing down of a wave path, such as light or sound, at the boundary between two different mediums with different densities. The deflection of a wave as it passes from one medium to another, eg through a lens.

Refractive errors

Visual problems that occur when the refractive structures of the eye fail to properly focus light rays on the retina.

Refractory period

A period of time after an action potential (AP) in a neuron when a second AP either cannot be produced or needs a much stronger stimulus to produce an AP.
The refractory period for production of an AP by a neuron occurs because voltage-gated Na+ channels possess the property of refractoriness whereby, once opened, they cannot then be subsequently opened for some time. Immediately after one AP all voltage-gated Na+ channels are refractory, creating an Absolute Refractory Period when a second AP cannot be produced no matter how strong a second stimulus.  This is followed by a Relative Refractory Period during which voltage-gated Na+ channels are recovering at different rates from refractoriness; during this period, the ability of a second stimulus to produce a second AP improves (i.e., the threshold to produce a second AP decreases with time).


Instrument that measures the refractive index of a liquid,

Regression analysis

A multivariate statistical analysis which attempts to determine if a term can be explained by one or more of other terms. And regression coefficient = The slope of the straight line that most closely relates two correlated variables. Regression was coined to describe the tendency of the quantitative traits of offspring to be closer to the population mean than are their parents' traits. It arises from a combination of factors - dominance, gene interactions, and environmental influences on traits.

Regular polygon

A polygon in which all the angles are equal and all of the sides are equal.

Regular polyhedron

A polyhedron whose faces are congruent, regular polygons.

Regulative development

A pattern of development, such as that of a mammal, in which the early blastomeres retain the potential to form the entire animal.

Regulator gene

A gene primarily involved in controlling another (structural) gene.  Genes that are involved in turning on or off the transcription of structural genes.

Regulatory regions or sequences

A DNA base sequence that controls gene expression.


Comprehensive program to reduce/overcome deficits following injury or illness, and to assist the individual to attain the optimal level of mental and physical ability.
Rehabilitation Counselor = Also called Vocational Counselor. A specialist in social and vocational issues who helps the patient develop the skills and aptitudes necessary for return to productive activity and the community.

Rehabilitation Facility = Agency of multiple, coordinated services designed to minimize for the individual the disabling effects of one's physical, mental, social, and/or vocational difficulties and to help realize individual potential.

Rehabilitation Nurse = A nurse specializing in rehabilitation techniques as well as basic nursing care. Nurses assist the patient and family in acquiring new information, developing skills, achieving competence and exhibiting behaviors that contribute to the attainment of a healthy state.

Reiter syndrome

A chronic form of inflammatory arthritis wherein the following three conditions are combined: (1) arthritis ; (2) inflammation of the eyes (conjunctivitis); and (3) inflammation of the genital, urinary or gastrointestinal systems.


Two clades are more closely related when they share a more recent common ancestor between them than they do with any other clade.


A set of ordered pairs.

Relative activity

Relative activity is an arbitrary response value to which the raw response of the tracer activity sample average is adjusted to remove signal variation.
The relative activity is divided by the average raw response of the tracer activity baseline standard to calculate a multiplying factor for each assay run. All raw responses in an assay run are multiplied by the assay's multiplying factor to yield the adjusted response. The variation in the raw response of the tracer activity between assay runs is due to signal variation and is not a component of the variation in the ligand-binder reaction. Adjusting the raw responses to the adjusted responses factors out the signal variation and only the binding variation remains

Relative atomic mass (RAM)

The mass of an atom relative to one atom of carbon. Carbon has a RAM of 12.

Relative efficacy

Stephenson (1956) originally proposed a numerical definition of agonist efficacy in which a pure antagonist (i.e. one totally devoid of any agonist activity) was defined as having zero efficacy, and a drug with an efficacy of 1 would, by definition, produce a maximal response at full occupancy that was 50% of the maximal response to a high-efficacy agonist. A more practical method of comparing agonist efficacy is to determine relative efficacy, i.e. to compare the ratio of the receptor occupancy at which two agonists produce the same response. There is no upper limit on the numerical value of efficacy or relative efficacy. See intrinsic efficacy.

Relative fitness

The contribution of one genotype to the next generation compared to that of alternative genotypes for the same locus.

Relative potency

The ratio of the potency of a test drug (i.e. its EC50, IC50, etc.) to that of a standard drug.


The relative values of time, motion, mass and energy of a body in motion.

Relay neuron

Neuron that transmits signals between different regions of the central nervous system

Release factors (RF1 and RF2)

Proteins in prokaryotes responsible for termination of translation and release of the newly synthesized polypeptide when a nonsense codon appears in the A site of the ribosome.  Replaced by eRF in eukaryotes.


A signal stimulus that functions as a communication signal between individuals of the same species.

Releasing hormone

A hormone produced by neurosecretory cells in the hypothalamus of the vertebrate brain that stimulates or inhibits the secretion of hormones by the anterior pituitary.

Reliability (in statistical tests)

Dependability of statistical tests.


If m = nq + r, then m/q has quotient q and remainder r.


Of (pertaining to) the kidney

Renal interstitial hydrostatic pressure (RIHP)

The pressure within kidney tissue, at sites other than within the blood vessels or kidney tubules.

Renal sympathetic nerve activity

The level of electrical activity in the nerves that control kidney function.
This activity can be measured by placing an electrode around the nerve.

Renin/angiotensin system (RAS)

The various components that lead to the production of angiotensin II, mediate the actions of angiotensin II, and lead to breakdown of angiotensin II.

Repeating decimal

A decimal in which the digits endlessly repeat a pattern.

Repeat region

The part of DNA where a certain codon is repeated many times. Expansions sometimes occur during replication of repeat regions. In Huntington’s Disease, the repeat region involves the CAG codon.

Repeat sequences

The length of a nucleotide sequence that is repeated in a tandem cluster.

Repetitive DNA

Nucleotide sequences, usually noncoding, that are present in many copies in a eukaryotic genome. The repeated units may be short and arranged tandemly (in series) or long and dispersed in the genome.A surprising portion of any genome consists not of genes or structural elements, but of frequently repeated such simple sequences.These may be short repeats just a few nucleotides (nt) long, like CACACA etc, or can range up to a few hundred nt long. Examples of the latter include Alu repeats, LINEs, SINEs. The function of these elements is often unknown. In shorter repeats like di- and tri-nucleotide repeats, the number of repeating units can occasionally change during evolution and descent. They are thus useful markers for familial relationships and have been used in paternity testing, forensic science and in the identification of human remains.


1. Repitition of a test or protocol to examine if it possible to get the same result.
2. DNA synthesis; the process of copying
A core tenet of science is that the data can be replicated by another experimenter using the same type of equipment and protocol.

Replication fork

The point at which the two strands of DNA are separated to allow replication of each strand. A Y-shaped point on a replicating DNA molecule where new strands are growing.

Replicative transposition

The transposition of a transposable element to a new location without it being lost from the original location.


A chromosomal region whose replication is controlled by a single adjacent DNA replication initiation site.  A genetic unit of replication including a length of DNA and its site for initiation of replication.


The DNA-replicating structure at the replication fork consisting of two DNA polymerase III enzymes and a primosome (primase and DNA helicase).

Reporter gene

Gene which codes for an easily measured protein product and is fused downstream of the gene of interest in order to assess the activity in the region upstream of the reporter gene.  Colorimetric and fluorimetric reporters also can be conjugated to probes to monitor biological events.

Report Logs

Report logs are files in which summary information from several different program operations are recorded.

Repressible enzyme

An enzyme whose synthesis is inhibited by a specific metabolite.

Repressible operon

Synthesis of a coordinated group of enzymes, involved in a single synthetic (anabolic) pathway, is repressible if excess quantities of (usually) the end product of the pathway leads to cessation of transcription of the genes encoding the enzymes of the pathway.


A protein that suppresses the transcription of a gene.

Repressor protein

The protein product of a regulator gene that acts to control transcription of inducible and repressible operons. A molecule that binds to the operator and prevents transcription of an operon. Generally any molecule that can reversibly inactivate a gene.


Reproduction is the process by which a new organism is produced; The manufacture of offspring as part of an organism's life cycle. Reproduction may be sexual, involving the fusion of gametes, or asexual. The first stage in the production of any organism is the fertilisation of an ova by spermatozoa (or spores on the case of plants).  Fertilisation produces a single cell called a zygote which contains all the information required to build the adult organism.  The progression (growth) from zygote to adult is achieved through cell division.

Reproductive cloning

The process of using somatic cell nuclear transfer (SCNT) to produce a normal, full grown organism (e.g., animal) genetically identical to the organism (animal) that donated the somatic cell nucleus. In mammals, this would require implanting the resulting embryo in a uterus where it would undergo normal development to become a live independent being. The first animal to be created by reproductive cloning was Dolly the sheep, born at the Roslin Institute in Scotland in 1996.

Reproductive isolation

Two populations of organisms are isolated if their members are unable to interbreed and produce fertile offspring.Various structural, behavioral, and biochemical features can prevent interbreeding and thus reproductively isolate populations as distinct species.

Repulsion (in genetics)

Allelic arrangement of two linked heterozygous loci, in which each homologous chromosome has one mutant (a or b) and one wild-type (A or B) allele (ie. Ab/aB).
Two linked heterozygous gene pairs in the arrangement, Ab/aB.


The surgical removal of part of a structure, such as bone.


a pond, lake, or basin, either natural or artificial, for the storage, regulation, and control of water.

Residual schizophrenia

A condition manifested by persons with signs of
schizophrenia who, following a psychotic schizophrenic episode, are no longer psychotic.


Opposition to current flow in a conductor.

Resolution (in DNA technology)

Degree of molecular detail on a physical map of DNA, ranging from low to high.

Resolving power

(1) The ability of an experimental technique to distinguish between two experimental conditions.
(2) A measure of the clarity of an image.
(1) This is typically discussed when one condition is rare and of particular interest or when the distributions of the two conditions are very close when it is necessary to have great confidence in the ability to differentiate between them.
(2) Measured as the minimum distance that two points can be separated and still be distinguished as two separate points.


A state where the natural frequency of a body equals an applied frequency.


The removal of bone tissue by normal physiological process or as part of a pathological process such as an infection.

Resource partitioning

The division of environmental resources by coexisting species populations such that the niche of each species differs by one or more significant factors from the niches of all coexisting species populations.


(1) In aerobic organisms, the intake of oxygen and the liberation of carbon dioxide.
(2) In cells, the oxygen-requiring stage in the breakdown and release of energy from fuel molecules.

Respiratory distress syndrome (RDS) (also known as Hyaline membrane disease, HMS)

A lung disease that occurs primarily in premature infants; the newborn must struggle for each breath and blueing of its skin reflects the baby's inability to get enough oxygen. It can also affect adults. In respiratory distress ineffective lung-gas exchange results which leads to insufficient oxygenation of the blood. It is among the most frequent cause of death in the premature infant as well as the most common illness in many neonatal intensive care units. The usual signs are labored, grunting respirations and poor oxygenation of body tissues in room air. Infants with severe RDS are at risk for developing a chronic lung disorder known as bronchopulmonary dysplasia (BPD).


A portable medical device used to measure inspired or expired volumes at the bedside.

Response code

In survey research, typically, responses to questions are "coded" by assigning numeric codes to each possible response. Thus a "yes" might be coded "1" and a "no" "2"; female respondents might be indicated by a "1" and male respondents by a "2"; each state or county might be assigned a numeric code

Response element

By definition, a portion of a gene which must be present in order for that gene to respond to some hormone or other stimulus. Response elements are binding sites for transcription factors. Certain transcription factors are activated by stimuli such as hormones or heat shock. A gene may respond to the presence of that hormone because the gene has in its promoter region a binding site for hormone-activated transcription factor. Example: the glucocorticoid response element (GRE).

Response Expression (in assays)

The response expression is one of five forms of the sample response which is used to calculate the y-axis of standard curve and to compute all sample concentrations (x-axis). The five response expressions are the adjusted response, the normal response, the log (base e) of the adjusted response, the log (base e) of the normalized response, and the logit response.

Resting Membrane Potential (RMP or EM)

A difference in electrical charge (i.e, a potential difference, pd) across the cell membrane of neurons, muscle cells, receptor cells and many other cells in the body.
A difference in charge across the cell membrane that arises because the cell membrane is selectively permeable, i.e., it allows trans-membrane diffusion of certain molecules but not others. Generally the RMP is such that the inside of the cell is negatively charged with respect to the outside (i..e, there is a net excess of negative charge inside the cell compared to the outside, just across the cell membrane). The word “Resting” indicates that this difference in charge is present even when the cell is quiescent and not undergoing any major change in activity levels.
In many cells, the RMP is due to the greater permeability of the cell membrane to K+ which, being at higher concentrations inside most cells, then will tend to diffuse out of the cell.  However, it is important to note that the RMP is not just a simple diffusion potential. Rather, it is largely a diffusion potential with an added component of a few millivolts owing to the direct polarising effect of the electrogenic sodium/potassium (Na+/K+) pump which pumps K+ back into the cell and Na+ out of the cell.  The pumping of these two ions is done in the ration of 3:2 and hence the pump contributes to the RMP.When the cell membrane is permeable to > 1 ion, the movement of all permeating ions needs to be considered and the RMP depends on different membrane permeabilities of the permeating ions and differences in their ionic concentration.As a general rule of thumb for the sign or polarity of a diffusion potential: The more mobile ion confers its sign on the region to which it is diffusing.
(see also Equilibrium potential, Goldman equation, and Nernst equation)

Resting tremor

Rhythmical movements present at rest and may be diminished during voluntary movement. Compare to Intention tremor.

Restriction (of a gene)

To "restrict" DNA means to cut it with a restriction enzyme.

Restriction endonuclease

A class of enzymes that cleave (i.e. cut) DNA at a specific and unique internal location along its length.Endonuclease that recognizes a particular short DNA sequence which they cleave. These enzymes are naturally produced by bacteria that use them as a defense mechanism against viral infection. The enzymes chop up the viral nucleic acids and hence their function is destroyed. They help to protect cells from viral infection and are used in work with DNA. Discovered in 1970 by Werner Arber, Hamilton Smith, and Daniel Nathans, restriction endonucleases are an important tool in genetic engineering, enabling the biotechnologist to splice new genes into the location(s) of a molecule of DNA where a restriction endonuclease has created a gap (via cleavage of the DNA).

Restriction enzymes

A degradative enzyme that recognizes and cuts up DNA (including that of certain phages) that is foreign to a bacterium.
A series of enzymes ("restriction endonucleases"), generally isolated from bacteria, which are able to recognize, attach to, specific, short nucleotide sequences and cut DNA molecules at those sequences ("restriction sites") and cut both strands of DNA at those sites.
An endonuclease that will recognize a specific target nucleotide sequence in DNA and break the DNA chain at the target; a variety of these enzymes are known, and they are extensively used in genetic engineering. Bacteria produce restriction enzymes for protection against invasion by foreign DNA such as phages. The bacteria's own DNA is modified in such a way as to prevent it from being clipped.
For example, the restriction enzyme BamHI locates and cuts any occurrence of:


Note that both strands contain the sequence GGATCC, but in antiparallel orientation. The recognition site is thus said to be palindromic, which is typical of restriction sites. Every copy of a plasmid is identical in sequence, so if BamHI cuts a particular circular plasmid at three sites producing three "restriction fragments", then a million copies of that plasmid will produce those same restriction fragments a million times over. There are more than six hundred known restriction enzymes. Bacteria contain over 400 such enzymes that recognize and cut over 100 different DNA sequences.

Restriction enzyme cutting site

A specific nucleotide sequence of DNA at which a particular restriction enzyme cuts the DNA. Some sites occur frequently in DNA (e.g., every several hundred base pairs), others much less frequently (rare- cutter; e.g., every 10,000 base pairs).

Restriction fragment

The piece of DNA released after restriction digestion of plasmids or genomic DNA. See Restriction enzyme. One can digest a plasmid and isolate one particular restriction fragment (actually a set of identical fragments). The term also describes the fragments detected on a genomic blot which carry the gene of interest.

Restriction fragment length polymorphism (RFLP)

Differences in DNA sequence on homologous chromosomes that result in different patterns of restriction fragment lengths (DNA segments resulting from treatment with restriction enzymes); useful as genetic markers for making linkage maps.
Variation in DNA fragment banding patterns of electrophoresed restriction digests of DNA from different individuals of a species.
Often due to the presence of a restriction enzyme cleavage site at one place in the genome in one individual and the absence of that specific site in another individual, i.e., are usually caused by mutation at a cutting site.
Although two individuals of the same species have almost identical genomes, they will always differ at a few nucleotides. Some of these differences will produce new restriction sites (or remove them), and thus the banding pattern seen on a genomic Southern will thus be affected. For any given probe (or gene), it is often possible to test different restriction enzymes until you find one which gives a pattern difference between two individuals - a RFLP. The less related the individuals, the more divergent their DNA sequences are and the more likely you are to find a RFLP.
Variation between individuals in DNA fragment sizes cut by specific restriction enzymes; polymorphic sequences that result in RFLPs are used as markers on both physical maps and genetic linkage maps.
See also Variable-number-of-tandem-repeats (VNTR) locus.

Restriction map

A diagram that shows restriction sites (i.e., where a restriction enzyme cleaves DNA) in relation to one another; A physical map of a piece of DNA showing recognition sites of specific restriction endonucleases separated by lengths marked in numbers of bases.
A "cartoon" depiction of the locations within a stretch of known DNA where restriction enzymes will cut.

The map usually indicates the approximate length of the entire piece (scale on the bottom), as well as the position within the piece at which designated enzymes will cut. This map happens to be of a plasmid, and the two ends are joined together with about 25 nt between the EcoRI and HindIII sites.

Restriction site

A specific sequence on a DNA strand that is recognized as a "cut site" by a restriction enzyme.

Reticular formation

A brain circuit involved with alertness and direction of attention to selected events; consists of a loose network of interneurons running through the brainstem, plus certain neurons in the thalamus that function as an extension of this network.


Joining of separate lineages on a phylogenetic tree, generally through hybridization or through lateral gene transfer. Fairly common in certain land plant clades; reticulation is thought to be rare among metazoans.


Long thread-like pseudopodia that branch apart and rejoin, forming a fine network.  They are characteristic of forams.


A fine network (e.g., endoplasmic reticulum).


The innermost layer of the vertebrate eye, containing photoreceptor cells (rods and cones) and neurons. It contains the cells that convert the light from the images formed by the lens into a biological response (a receptor potential) that ultimately leads to the production of Action Potentials in optic nerv fibres that transmit this information to the brain.


The light-absorbing pigment in rods and cones of the vertebrate eye. A derivative from vitamin A which is why vitamin A deficiency can lead to problems in vision.

Retinitis pigmentosa (RP)

A hereditary, slowly degenerative disease of the retina, beginning in childhood and resulting in serious impairment of vision or possible blindness in middle age.


A malignant tumor in the retina. Predisposition to retinoblastoma is inherited as an autosomal dominant. A childhood cancer of retinoblast cells caused by the inactivation of an anti-oncogene.

Retinopathy of prematurity (ROP)

Injury to the blood vessels of retina due to oxygenation changes, asphyxia, shock, and other stresses at the time of birth. There is a higher incidence in extremely low birth weight babies. Previously known as retrolental fibroplasia.

Retrocochlear deafness

Hearing loss resulting from damage at some site after the cochlea (i.e., in the central nervous system).

Retrograde Amnesia

Inability to recall events that occurred prior to the accident; may be a specific span of time or type of information.

Retrotransposon (retroposon)

A class of genetic elements that includes retroviruses and transposons that have an intermediate RNA stage. A transposon that was created by reverse transcription of an RNA molecule.

Retroviral vector

Artificial DNA construct derived from a retrovirus, used to insert sequences into an organism's chromosomes. Certain retroviruses that are used by genetic engineers to carry new genes into cells. These molecules become part of that cell's protoplasm.


Viruses consist of a nucleic acid (DNA or RNA) enclosed in a protein coat (a “capsid”). Retroviruses also include the enzyme reverse transcriptase with the viral RNA.An RNA virus that reproduces by transcribing its RNA into DNA and then inserting the DNA into a cellular chromosome; an important class of cancer-causing viruses.From the Latin word retrovir, which means "backward man".
Oncogenic (i.e., cancer-producing), single-stranded, diploid RNA (ribonucleic acid) viruses that contain (+) RNA in their virions and propagate through a double-helical DNA intermediate. They are known as retroviruses because their genetic information flows from RNA to DNA (reverse of normal). That is, the viruses contain an enzyme that allows the production of DNA using RNA as a template.
Reverse transcriptase makes a single-stranded viral DNA copy of the single-stranded viral RNA. The single stranded viral DNA is subsequently turned into a double-stranded DNA. In the process of making the cDNA strand for the viral RNA, the enzyme also makes long terminal repeats (LTRs) sequences at the terminal ends of the cDNA. These LTRs may also make insertion of the viral DNA into the host DNA easier. The inserted viral DNA makes RNA transcripts which are packaged with viral protein coats and reverse transcriptase.When the viral DNA immediately takes over the host cell it begins making new viruses which eventually cause the rupture (lysis) of the cell, releasing those new viruses to continue the infection cycle. This cycle occurs when the viral DNA is incorporated into the host DNA as a prophage. When the cell replicates the prophage is passed along as if it were host DNA. Sometimes the prophage can emerge from the host chromosome and enter the lytic cycle spontaneously once every 10,000 cell divisions. Ultraviolet light and x-rays may also trigger emergence of the prophage. Retroviruses can only infect cells in which DNA is replicating, such as tumor cells (since they are constantly replicating) or cells comprising the lining of the stomach (since that lining must replace itself every few days).

Return flow

1) That part of a diverted flow that is not consumptively used and returned to its original source or another body of water. (2) (Irrigation) Drainage water from irrigated farmlands that re-enters the water system to be used further downstream.

Return flow(Irrigation)

irrigation water that is applied to an area and which is not consumed in evaporation or transpiration and returns to a surface stream or aquifer.

Reversal (character reversal)

The re-establishment of an ancestral character state through the loss of an evolutionary novelty (apomorphy). For example, winged insects (Pterygota) evolved from a wingless ancestor; however, some pterygote lineages have subsequently lost their wings, e.g., fleas, lice, some grasshoppers and beetles.

Reverse osmosis

The process of removing salts from a solution (such as water) using a membrane. With reverse osmosis, the product water passes through a fine membrane that the salts are unable to pass through, while the salt waste (brine) is removed and disposed. This process differs from electrodialysis, where the salts are extracted from the feedwater by using a membrane with an electrical current to separate the ions. The positive ions go through one membrane, while the negative ions flow through a different membrane, leaving the end product of freshwater.

Reverse Transcriptase

An enzyme, encoded by some RNA viruses, requiring a DNA primer, that catalyzes the synthesis of a DNA strand from an RNA template.  An enzyme that can use RNA as a template to synthesize DNA. It will make a DNA copy of an RNA template - a DNA-dependant RNA polymerase. RT is used to make cDNA; one begins by isolating polyadenylated mRNA, providing oligo-dT as a primer, and adding nucleotide triphosphates and RT to copy the RNA into cDNA.

Reverse Transcriptase Polymerase Chain Reaction (RT-PCR)

A variation of the Polymerase Chain Reaction (PCR) technique in which cDNA is made from RNA via reverse transcription. The cDNA is then amplified using standard PCR protocols.

Reverse Transcription

The process of copying information found in RNA into DNA.

Rexed laminae

A series of morphologically different areas of the spinal cord grey matter

Reye’s syndrome

A rare and serious brain and liver disorder that is associated with the use of aspirin in children.

Reynold’s number

Dimensionless number relating the ratio of inertial to viscous forces, to predict flow patterns. Explicitly, the Reynolds number is Re=UL/\nu in which U and L are characteristic velocity and length scales, respectively, and \nu is the kinematic viscosity.

R group

Used to denote virtually any organic substituent (the R groups of amino acids, for example).


Movement of an organism in response to the motion of a current of water or air.


Growth or orientation of an organism, or of part of an organism, in response to the motion of a current of water or air.

Rheumatoid arthritis

Generalized inflammatory joint disease. An autoimmune disease which causes chronic inflammation of the joints, the tissue around the joints, as well as other organs in the body. Autoimmune diseases occur when the body tissues are mistakenly attacked by its own immune system. The immune system is a complex organization of cells and antibodies designed normally to "seek and destroy" invaders of the body, particularly infections. Patients with these diseases have antibodies in their blood which target their own body tissues, where they can be associated with inflammation. Because it can affect multiple other organs of the body, rheumatoid arthritis is referred to as a systemic illness and is sometimes called rheumatoid disease. While rheumatoid arthritis is a chronic illness (meaning it can last for years) patients may experience long periods without symptoms.


A subspecialty of internal medicine that involves the non-surgical evaluation and treatment of the rheumatic diseases and conditions. Rheumatic diseases and conditions are characterized by symptoms involving the musculoskeletal system. Many of the rheumatic diseases and conditions feature immune system abnormalities. Therefore, rheumatology also involves the study of the immune system. Classical rheumatology training includes 4 years of medical school, 1 year of internship in internal medicine, 2 years of internal medicine residency, and 2 years of rheumatology fellowship. There is a subspecialty board for rheumatology certification. The American College of Rheumatology is the official organization acting on behalf of the field of rheumatology in the United States.

Rheumatic heart disease

A condition that ensues from rheumatic fever wherein the muscles, valves, or lining of the heart may become inflamed and then permanently damaged.


The most prevalent nasal disease, and characterized by nasal mucous membrane inflammation. Can be infectious or noninfectious. Infectious rhinitis usually results from viral infection, which may trigger a secondary bacterial infection. There are three noninfectious rhinitis subtypes: seasonal allergic rhinitis, perennial allergic rhinitis, and perennial nonallergic rhinitis.


Reconstructive surgery of the nose to correct deformities or for cosmetic purposes.


Interruption of a spinal root within the spinal canal.


A visual pigment consisting of the light-absorbing molecule (the pigment) retinal, and the protein molecule, opsin. When rhodopsin absorbs light, the retinal changes shape and dissociates from the opsin, after which it is converted back to its original form.

Rho protein

A protein factor required to recognize certain transcription termination signals in Escherichia coli.

Rho-dependent terminator

A DNA sequence signaling the termination of transcription; termination requires the presence of the rho protein. And Rho-independent terminator = A DNA sequence signaling the termination of transcription; the rho protein is not required for termination.


An anti-Rh gamma globulin medication used to combat incompatibility in blood type between a mother and her fetus.


One of the 12 paired arches of bone which form the skeletal structure of the chest wall (the rib cage). The ribs attach to the building blocks of the spine (vertebrae) in the back. The 12 pairs of ribs consist of:

  • True ribs: The first seven ribs attach to the sternum (the breast bone) in the front and are known as true ribs (or sternal ribs).
  • False ribs: The lower five ribs do not directly connect to the sternum and are known as false ribs.

Ribonuclease (RNase)

An enzyme which degrades RNA. It is ubiquitous in living organisms and is exceptionally stable. The prevention of RNase activity is the primary problem in handling RNA.

Ribonucleic acid (RNA)

A single-stranded nucleic acid similar to DNA but having ribose sugar rather than deoxyribose sugar and uracil rather than thymine as one of the pyrimidine bases;     A type of nucleic acid consisting of nucleotide monomers with a ribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U); usually single-stranded; functions in protein synthesis and as the genome of some viruses.
RNA is found in the nucleus and cytoplasm of cells and plays an important role in protein synthesis and other chemical activities of the cell. The structure of RNA is similar to that of DNA. There are several classes of RNA molecules, including messenger RNAtransfer RNAribosomal RNA. All are involved in the synthesis of proteins from the information contained in the DNA molecule and other small RNAs, each serving a different purpose.
Ribonucleotide = nucleotide in which a purine or pyrimidine base is linked to a ribose molecule.

RNA splicing

RNA splicing is performed by small nuclear RNAs (snRNAs) complexed to protein subunits to form small nuclear ribonuclear proteins (snRNPs) which are transported into the nucleus to catalyse alternative splicing. These form the core of the spliceosome: the cellular machinery responsible for pre-mRNA editing. Additional molecular components involved in RNA transcription and processing segregate to subnuclear structures such as Cajal bodies and gemini of coiled-bodies (gems). SMN is expressed in the cytoplasm, but also in the nucleus, where it localises to Cajal bodies and gems. SMN binds seven additional proteins, Gemins 2-7 and unr interacting protein (Unrip), to form the "SMN complex" which provides an assembly platform for the spliceosome. The SMN complex mediates binding of specific uridine-rich snRNAs to their partners, Sm core proteins, forming snRNPs. SMN also interacts with RNA polymerase II and small nucleolar RNPs, consistent with roles in transcription and ribosome formation. Finally, SMN modulates the RNA interference (RNAi) pathway since Gemins 3 and 4 associate with microRNP complexes and titrate away from the SMN complex. All the functions described in the previous paragraph require SMN to be located in the nucleus. Most proteins require active transport into the nucleus, which is mediated by the nuclear pore complex (NPC). Proteins to be transported, such as SMN, have nuclear recognition sequences which bind to cytosolic nuclear import receptors, importin-α and importin-β (IMP). This trimeric complex is transported across the NPC by binding to four key nucleoporins (Nup) and phosphorylation of the small GTPase Ran. Exit from the nucleus occurs in the reverse involving exportin (EXP) binding to nuclear export sequences within proteins and Ran GTPase activity. In addition to a cytoplasmic targeting sequence, SMN binding to heteronuclear RNPs (hnRNPs) also mediates its nuclear to cytoplasmic shuttling: hnRNP binding is the same mechanism used by spliced mRNAs destined for ribosomes.


A strand of RNA synthesized in-vitro (usually radiolabeled) and used as a probe for hybridization reactions. An RNA probe can be synthesized at very high specific activity, is single stranded (and therefore will not self anneal), and can be used for very sensitive detection of DNA or RNA.


The sugar component of RNA.


A cellular organelle composed of proteins plus ribosomal RNA (rRNA), that catalyzes translation of messenger RNA (mRNA) into an amino acid sequence.
Ribosomes are a complex, constructed in the nucleus, made up of two non-identical subunits each consisting of a different rRNA and a different set of proteins. The rRNA and protein molecules make up the two subunits of ribosomes. They are the cellular site at which proteins are manufactured.

Ribosomal RNA (rRNA)

A class of RNA molecules, coded in the nucleolar organizer, that have an integral (but poorly understood) role in ribosome structure and function.  RNA components of the subunits of the ribosomes. They are the most abundant RNA in the cell (on a mass basis). Together with proteins, they form the structure of ribosomes that coordinate the sequential coupling of tRNA molecules to the series of mRNA codons.

Ribosomal ambiguity mutation (RAM mutation)

A ribosomal mutation that allows incorrect tRNAs to be incorporated into the translation process.

Ribosome binding site

The region of an mRNA molecule that binds the ribosome to initiate translation.


Riboswitches are RNA elements that bind metabolites and regulate gene expression.
Riboswitches are RNA elements that bind metabolites such as S-adenosylmethionine (SAM) and regulate gene expression. This regulation is typically in cis, where a riboswitch in a 5' untranslated region (UTR) modulates either transcription or translation of the downstream coding sequence.
Some bacterial SAM riboswitches can act as noncoding RNAs and regulate gene expression in trans. When bound to SAM, these RNAs directly bind to the 5' UTR of the virulence regulator PrfA in the human pathogen Listeria monocytogenes. This interaction downregulates PrfA expression and virulence gene expression.


Catalytic or autocatalytic RNA: An enzymatic RNA molecule that catalyzes reactions during RNA splicing. RNA with enzymatic activity.


Gauge to determine the sag of pectin gels.

Right angle

An angle whose measure is 90 degrees.

Right circular cone

A cone whose base is a circle located so that the line connecting the vertex to the center of the circle is perpendicular to the plane containing the circle.

Right circular cylinder

A cylinder whose bases are circles and whose axis is perpendicular to its bases.

Righting reactions or responses

Automatic adjustments made to a person's body to maintain an upright and preserve balance when moving from one position to another.

Right triangle

A triangle that contains a right angle.


Stiffness of a limb due to increased tone in both flexors and extensors.
See Spasticity

Riparian water rights

the rights of an owner whose land abuts water. They differ from state to state and often depend on whether the water is a river, lake, or ocean. The doctrine of riparian rights is an old one, having its origins in English common law. Specifically, persons who own land adjacent to a stream have the right to make reasonable use of the stream. Riparian users of a stream share the streamflow among themselves, and the concept of priority of use (Prior Appropriation Doctrine) is not applicable. Riparian rights cannot be sold or transferred for use on nonriparian land.

RNase protection assay

A sensitive method to determine (1) the amount of a specific mRNA present in a complex mixture of mRNA and/or (2) the sizes of exons which comprise the mRNA of interest. A radioactive DNA or RNA probe (in excess) is allowed to hybridize with a sample of mRNA (for example, total mRNA isolated from tissue), after which the mixture is digested with single-strand specific nuclease. Only the probe which is hybridized to the specific mRNA will escape the nuclease treatment, and can be detected on a gel. The amount of radioactivity which was protected from nuclease is proportional to the amount of mRNA to which it hybridized. If the probe included both intron and exons, only the exons will be protected from nuclease and their sizes can be ascertained on the gel.

RNA editing

The insertion of uridines into mRNAs after transcription is completed; controlled by guide RNA (gRNA).
May also sometimes involve insertion of cytidines and possible deletions of bases.

RNA in-situ hybridisation

A technique that is used to identify the spatial pattern of expression of a particular transcript (usually an mRNA). The probe is labeled, either radioactively or by chemically attaching a fluorochrome visualised by fluorescence or an enzyme that can convert a substrate to a visible dye. A tissue or organism is soaked in a solution of single-stranded probe under conditions that allow the probe to hybridize to complementary RNA sequences in the cells; unhybridized probe is then removed. Radioactive probe is detected by autoradiography. Fluorochrome is detected by fluorescence microscopy. Enzyme labeled probe is detected by soaking the tissue in the substrate; the dye develops in sites where the transcript of interest was expressed.

RNA interference (RNAi) (Also known as RNA silencing)

The mechanism by which small double-stranded RNAs can interfere with expression of any mRNA having a similar sequence: what happens when short strands of (complementary) double-stranded RNA (dsRNA) are introduced into living cells.
Those small RNAs are known as 'siRNA', for short interfering RNAs. The mode of action for siRNA appears to be via dissociation of its strands, hybridization to the target RNA, extension of those fragments by an RNA-dependent RNA polymerase, then fragmentation of the target. Importantly, the remnants of the target molecule appears to then act as an siRNA itself; thus the effect of a small amount of starting siRNA is effectively amplified and can have long-lasting effects on the recipient cell.
That interaction can be done either by physical insertion of the dsRNA or by genetic engineering of the organism so the organism's cell(s) themselves produce that (new) dsRNA. For example, genetic engineers can utilize T7 RNA polymerase to cause the production of such dsRNA within living cells.Viral infection (i.e., insertion of viral dsRNA) and also micro-RNAs can also cause RNA interference.
If those dsRNAs are relatively long, they are cleaved (cut) by enzymes known as dimeric RNase III ribonucleases [also called dicer enzymes] into segments approximately 19-21 bp (base pairs) in length; called siRNAs (short interfering RNAs or small interfering RNAs). That siRNA (i.e., specific to a selected gene's mRNA) causes specific cellular "cutting enzymes" in RISC (RNA-induced silencing complex) to adhere to the transcribed-from-gene mRNA which the dsRNA was chosen to be specific to. Those "cutting enzymes" cut-up and mark for destruction the transcribed-from-gene mRNA; thereby negating the effects of that gene. That effect is known as gene silencing, and it persists even in the (first generation) offspring of that affected organism. RNAi is one methodology which can be utilized to cause gene silencing/knockout. During 2002, Thomas A. Rosenquist and Gregory J. Hannon created "knockdown" mice via genetic engineering so those mice (continually) produced the dsRNA which silenced a selected gene. Later, the first-generation offspring of those knockdown mice also "silenced" that selected gene in their bodies. Under some conditions, RNAi can also inhibit gene transcription (i.e., causing formation of silent heterochormatin in some organisms).
The RNAi effect has been exploited in numerous research programs to deplete the call of specific messages, thus examining the role of those messages by their absence.

RNA phage

Phage whose genetic material is RNA.  The simplest known phages.

RNA polymerase (RNA transcriptase)

An enzyme that catalyzes the synthesis of an RNA strand from a DNA template. The enzyme that polymerizes RNA by using DNA as a template.
This enzyme links together the growing chain of ribonucleotides during transcription. It can also act as a primase initiating DNA replication.

RNA processing

Modification of RNA before it leaves the nucleus. This is a process unique to eukaryotes.

RNA replicase

A polymerase enzyme that catalyzes the self-replication of single-stranded RNA.

RNA splicing

The removal of noncoding portions (introns) of the RNA molecule after initial synthesis. RNA-processing step in which all of the intron sequences are removed and exon sequences are kept therebv producing a much shorter RNA molecule.

Rod cell

One of two kinds of photoreceptors in the vertebrate retina.  As it contains only one type of photopigment (rhodopsin) that is capable of absorbing light, information from rods cannot be used to differentiate different wavelengths of light – i.e., to tell colour.  They are very sensitive to light and therefore, while being non-functional in bright light conditions (such as in daylight), enable night vision. You use the rods to see the faint light of stars at night.

Rolling-circle replication

A model of DNA replication that accounts for a circular DNA molecule producing linear daughter double helices.


1. In biology: The root of a subtree of the Tree of Life is the branch that connects the subtree to the remainder of the Tree of Life.
2. In mathematics: The root of an equation is the same as the solution to the equation.
For a given group of organisms, the root is the branch that connects this group to its containing group.

Rooting response

A food-seeking movement which occurs in response to tactile input presented on the lips or cheeks characterized by mouth opening and head turning in the direction of the touch. It occurs until approximately 4 to 5 months of age; stronger just before feeding and when the infant is in a position generally associated with feeding

Rotation (of a bone)

Movement of a bone such that it revolves around it's own longitudinal axis (e.g. turning the head from side to side at the joint between the atlas and axis).
(see also Pronation and Supination)

Rough endoplasmic reticulum (RER)

That portion of the cell’s endoplasmic reticulum that is studded with ribosomes.


Rate of Perceived Exertion; a subjective measure of exercise intensity. The RPE requires the exerciser to think about how hard they feel their body is working against a standardized scale. The most common RPE scale used is called the Borg Scale. On the Borg scale there are numbers from 6 through 20. Each number corresponds to a certain level of intensity. Levels 6 to 11 are considered light intensity, moderate intensity would be 12 to 14, and vigorous would be 15 to 17. Maximum intensity would be 18 to 20. RPE takes into account how hard the entire body is working. It's not just about your legs getting tired or your feet being sore.  It takes in account breathing rate, heart rate, muscle fatigue and perspiration.  (see Borg scale)

R plasmid (R factor; resistance transfer factor)

A plasmid containing one or several transposons with resistance genes. A bacterial plasmid carrying genes that confer resistance to certain antibiotics. Plasmids carrying genes controlling resistance to various drugs.


The concept that in certain (r-selected) populations, a high reproductive rate is the chief determinant of life history.

Rubella (also known as German measles)

A disease caused by the rubella (little red) vbirus. Although usually a mild febrile disease it is in a major tragedy in pregnant women which can cause miscarriage or stillbirth, severe birth defects including blindness, deafness, and damage to heart, brain, and other organs. Childhood immunizations will protect persons from this disease.


Ribulose carboxylase, the enzyme that catalyzes the first step (the addition of CO2 to RuBP, or ribulose bisphosphate) of the Calvin cycle.

Rule out

A term much used in medicine, meaning to eliminate or exclude something from consideration. The ACB (albumin cobalt binding) test helps rule out a heart attack in the differential diagnosis of severe chest pain.


An animal, such as a cow or a sheep, with an elaborate, multicompartmentalized stomach specialized for an herbivorous diet.


--(1) That part of the precipitation, snow melt, or irrigation water that appears in uncontrolled surface streams, rivers, drains or sewers. Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or base runoff, and according to source as surface runoff, storm interflow, or ground-water runoff. (2) The total discharge described in (1), above, during a specified period of time. (3) Also defined as the depth to which a drainage area would be covered if all of the runoff for a given period of time were uniformly distributed over it.