General Genetics
Emporia State University

This glossary was created by Mackenzie Peterson ( as an undergraduate project during the Spring 1997 semester. This glossary is not meant to include all the words that might be included in a glossary of genetics, but only includes those terms that are mentioned in the notes for the class. The glossary is updated as the notes are updated.

       A  B  C  D  E  F  G  H  I  J  K  L  M

       N  O  P  Q  R  S  T  U  V  W  X  Y  Z

acentric fragment: a portion of a chromatid or chromosome that lacks a centromere

additive genetic variance: genetic variance atributed to the average effects of substituting one allele for another at a given locus, or at the multiple loci governing a polygenic trait

allele: one of a series of possible alternative forms of a given gene, differing in DNA sequence and affecting the functioning of a single product (RNA or protein)

allele frequency: the percentage of all alleles at a given locus in a population gene pool represented by a particular allele

allopolyploidy: the combination of genetically distinct chromosome sets that results in a polyploid organism

allosteric protein: a protein that may change its shape as a consequence of interaction with another molecule

allozygosity: having two homologous genes at one locus that are of independent origin, as far as can be determined from a pedigree

amino acid: any of the subunits that are polymerized to form proteins

amino-acyl tRNA synthetase: an enzyme that activates amino acids and attaches each activated amino acid to its own species of tRNA

aneuploidy: a condition in which the chromosome number of an individual is not an exact multiple of the typical haploid set for the species

anti-codon: the triplet of nucleotides in a transfer RNA molecule which associates by complementary base pairing with a specific triplet codon in the messenger RNA molecule during its translation in the ribosome

anti-parallel: the opposite strand orientations with which all nucleic acid duplexes associate; if one strand is oriented left to right 5' to 3', the complementary strand is oriented left to right 3' to 5'

A site: holds the incoming tRNA molecule charged with the next amino acid; the tRNAs are held so that the anticodons form base pairs with adjacent complementary codons of the mRNA moving through the ribosome

assortative mating: sexual reproduction in which there is a tendency for males of a particular kind to mate with females of a particular kind

attenuator: a nucleotide sequence that is located upstream of those bacterial operons which encode the enzymes that are involved in the synthesis of amino acids; controls transcription of operons

autopolyploid: a polyploid that originates by the multiplication of one basic set of chromosomes

autoradiograph: a photographic picture showing the position of radioactive substances in tissues, obtained by coating a squash preparation or a section with a photographic emulsion in the dark, and subsequently developing the latent image produced by the decay radiations

autosome: a chromosome other than a sex chromosome

autozygosity: having two homologous genes at a given locus that are identical by descent; both genes are derived from the same ancestor

auxotroph: a mutant microorganism that can be grown only upon minimal medium that has been supplemented with growth factors not required by wildtype strains

avirulent: having lost the ability to produce disease

Barr body: the condensed single X chromosome seen in the nuclei of somatic cells of female mammals

binomial theorem: the theorem that gives the terms of the expansion of a binomial expression raised a particular power

bivalent: a pair of homologous, synapsed chromosomes

bottleneck: a large population passes through a contracted stage and then expands again with an altered gene pool as a consequence of genetic drift; causes fluctuations in gene frequencies

CAAT box: part of a DNA sequence possibly involved in binding RNA polymerase

cAMP-CAP complex: composed of cyclic AMP and catabolite activator protein, this complex binds to a part of the promoter and enhances the affinity of RNA polymerase for the promoter

central dogma: the concept describing the functional interrelations between DNA, RNA, and protein; the direction of transmission is DNA-->RNA-->protein

centric fusion: breakage in the very short arms of two acrocentric chromosomes, followed by fusion of the long parts into a single chromosome; the two small fragments are usually lost; also known as a Robertsonian event or translocation

centrifuge: an apparatus used for the separation of substances by the application of centrifugal force generated by whirling at a high rate of rotation a vessel containing a fluid in which the substances are suspended

centrioles: a cylindrical cellular organelle that is found in eukaryotes; they migrate to the polar regions of the cell during mitosis and meiosis

centromere: a constricted region in eukaryotic chromosomes on which the kinetochore lies

chiasma: chiasmata, plural represents a point where non-sister chromatids exchanged genetic material during pachynema

chi-square: a statistical procedure that enables the investigator to determine how closely an experimentally obtained set of values fits a given theoretical expectation

chromatids: the two daughter strands of a duplicated chromosome that are joined by a single centromere; upon division of the centromeres, the sister chromatids become separate chromosomes

chromatin: the complex of nucleic acids and proteins comprising eukaryotic chromosomes

chromosome: the DNA that carries genetic information essential for life

chromosome mapping: the process of determining the locations of genes on chromosomes

cis configuration: the situation in which both mutant alleles of different genes are located on the same homologue; the wildtype alleles are located on the other homologue

coding strand: the strand of duplex DNA that has the same nucleotide sequence as mRNA except that T substitutes in DNA for U in RNA

codominant: designating genes when both alleles of a pair are fully expressed in the heterozygote

codon: the nucleotide triplet in messenger RNA that specifies the amino acid to be inserted in a specific position in the forming polypeptide during translation

coefficient of coincidence: an experimental value equal to the observed number of double crossovers divided by the expected number

colchicine: an alkaloid that inhibits the formation of the spindle and delays the division of centromeres; used to produce polyploid varieties of horticulturally important species; also used to stop mitosis at metaphase for preparation of karyotypes

congenital: existing at birth; may or may not be of genetic origin

conjugation: a temporary union of two single-celled organisms with at least one of them receiving genetic material from the other; in bacteria the exchange is unidirectional with the donor cell extruding all or a portion of one of its chromosomes into the recipient cell

conservative replication: a postulated mode of DNA replication in which an intact double helix acts as a template for a new double helix; known to be incorrect

covalent bond: a valence bond formed by a shared electron between the atoms in a covalent compound

crossing-over: the exchange of genetic material between homologous chromosomes during meiosis

deletion: the loss of a segment of the genetic material from a chromosome

denaturation: the loss of the native configuration of a macromolecule resulting from heat treatment, chemical treatment, etc.; this represents the dissociation of the double helix into its complementary strands

density gradient centrifugation: a technique of separation using a gradient of densities established by adding a high molecular weight salt such as cesium chloride; the mixture to be separated is layered in the gradient and then centrifuged until each molecule reaches the layer in the gradient with a density equal to its own

dicentric fragment: a chromosome or chromatid that has two centromeres

diploid: the state in which each type of chromosome (except the sex chromosomes) is represented twice (2N)

directional selection: selection resulting in a shift in the population mean in the direction desired by the breeder or in the direction of greater adaptation by nature

disassortative mating: the mating of two individuals with dissimilar phenotypes

dispersive replication: an obsolete model of DNA replication in which parental and newly synthesized daughter molecules are interspersed in an essentially random fashion

disruptive selection: the selection of divergent phenotypic extremes in a population until, after several generations of selection, two discontinuous strains are obtained

dizygotic twins: arise when two eggs are released and fertilized; no more genetically similar than ordinary siblings

DNA: deoxyribonucleic acid; the molecular basis of heredity; consists of a polysugar-phosphate backbone from which the purines and pyrimidines project

DNA polymerase: an enzyme that catalyzes the formation of DNA from deoxyribonucleoside triphosphates using single-stranded DNA as a template; three different DNA polymerases are known to exist

dominant trait: a trait controlled by an allele that expresses itself even when heterozygous

double cross-over: breakage and interchange occurring twice within a tetrad involving two, three, or four of the chromatids

double helix: the Watson-Crick model of DNA structure, involving coiling of two hydrogen-bonded polynucleotide, antiparallel strands wound into a right-handed spiral configuration

double transformant: a bacteria that has simultaneously transformed two or more genes; the genes cotransformed are inferred to be closely linked because transforming DNA fragments are usually small

elongation factor: a protein that complexes with ribosomes to promote elongation of polypeptide chains

endonuclease: an enzyme that breaks the internal phosphodiester bonds in a DNA molecule

episome: a class of genetic elements; F factor is an example; compare with plasmid

epistasis: the nonreciprocal interaction of nonallelic genes; the situation in which one gene masks the expression of another

equilibrium population: a population in which the allelic frequencies of its gene pool do not change through successive generations

euchromatin: regions of eukaryotic chromosomes that are diffuse during interphase; presumably the actively transcribing DNA of the chromosomes

eukaryote: an organism with cells that contain true nuclei with nuclear membranes

euploidy: a polyploid cell or organism whose chromosome number is an exact multiple of the basic number of the species from which it originated

evolution: genetic changes within a genealogical lineage producing speciation

exon: a portion of the split gene that is included in the transcript of a gene and survives processing of the RNA in the cell nucleus to become part of a spliced messenger of a structural RNA in the cell cytoplasm

exonuclease: an enzyme that digests DNA, beginning at the ends of the strands

expressivity: the range of phenotypes expressed by a given genotype under any given set of environmental conditions, or over a range of environmental conditions

F+ cell: a bacterial cell possessing a fertility factor in a plasmid; this cell can act as a donor during conjugation

F- cell: a bacterial cell devoid of an F factor and that therefore can act only as a recipient during conjugation

fecundity: potential fertility or the capability of repeated fertilization; specifically refers to the quantity of gametes produced per individual over a period of time

fertility factor: a supernumerary sex chromosome that determines the sex of E. coli; in the presence of the F episome, the bacterium functions as a male

fitness: the relative ability of an organism to survive and transmit its genes to the next generation

fixation: the status of a locus in which all members of a population are homozygous; the frequency of the fixed allele is 1.0

founder effect: the principle that when a small sample of a larger population establishes itself as a newly isolated entity, its gene pool carries only a fraction of the genetic diversity represented in the parental population

fundamental number: the number of chromosome arms in a somatic cell of a particular species

gametic selection: the forces acting to cause differential reproductive success of one allele over another in a heterozygote

gene: a hereditary unit that occupies a specific position within the genome; it has one or more specific effects upon the phenotype of the organism; it can mutate to various allelic forms

genetic code: the consecutive nucleotide triplets of DNA and RNA that specify the sequence of amino acids for protein synthesis

genetic counseling: the analysis of risk of producing genetically defective offspring within a family, and the presentation to family members of available options to avoid or ameliorate possible risks

genetic drift: the random fluctuations of gene frequencies due to sampling errors; while drift occurs in all populations, its effects are most evident in very small populations

genome: a term used to refer to all of the genes carried by a single gamete

genotype: the genetic constitution of an organism, as distinguished from its physical appearance

genotypic frequency: the proportion of individuals in a population that possess a given genotype

GTP: an energy-rich molecule analogous to ATP that is required for the synthesis of all peptide bonds during translation

haploid: the genetic chromosome number; the state in which each type of chromosome is represented only once (N)

Hardy-Weinberg law: the concept that both gene frequencies and genotype frequencies will remain constant from generation to generation in an infinitely large, interbreeding population in which mating is at random and there is no selection, migration, or mutation

helicase: an enzyme that unwinds a DNA double helix molecule ahead of DNA polymerase III

hemizygous: the condition of loci on the X chromosome of the heterogametic sex of a diploid species

heritability: an attribute of a quantitative trait in a population that expresses how much of the total phenotypic variation is due to genetic variation

hermaphroditic: having both male and female reproductive organs

heterochromatin: chromatin that remains tightly coiled and darkly staining throughout the cell cycle

heterogametic: the sex that produces gametes containing unlike sex chromosomes

heteromorphic: the state of having homologous chromosomes that differ morphologically

heterozygote advantage: the situation where the heterozygote has a greater fitness than either homozygote

heterozygous: having different alleles in the corresponding loci of homologous chromosomes

homogametic: the sex with homomorphic sex chromosomes; it produces only one kind of gamete in regard to the sex chromosomes

homologous chromosomes: chromosomes that pair during meiosis; they contain the same linear sequence of genes, presenting each gene in duplicate

homomorphic: morphologically identical members of a homologous pair of chromosomes

homozygous: having identical alleles in the corresponding loci of homologous chromosomes and therefore breeding true

hybrid: a heterozygote; an offspring from genetically dissimilar parents, even different species

hydrogen bond: the weak electrostatic attraction that exists between a hydrogen atom that is covalently bonded to an O or N atom and an atom containing an unshared electron pair

inbreeding: the crossing of closely related plants or animals

inbreeding coefficient: the probability that two allelic genes united in a zygote are both descended from a gene found in an ancestor common to both parents; also the proportion of loci at which an individual is homozygous

incomplete dominance: failure of a dominant phenotype to be fully expressed in an organism carrying a dominant and a recessive allele; the result is usually an intermediate between the homozygous dominant and the recessive forms

inducible system: a regulatory system in which the product of a regulator gene is active and blocks transcription of the operon

initiation factor: a protein required for the initiation of protein synthesis

intron: in split genes, a segment that is transcribed into nuclear RNA, but is subsequently removed from within the transcript and rapidly degraded

inversion: chromosome segments that have been turned through 180 degrees with the result that the gene sequence for the segment is reversed with respect to that of the rest of the chromosome

karyotype: the number, size, and morphology of the chromosome set of a cell, individual, or species

kinetochore: the chromosomal point of attachment for spindle fibers during mitosis and meiosis; located on the centromere

lagging strand: the discontinuously synthesized strand of DNA containing ligated Okazaki fragments

leading strand: the DNA strand synthesized with few or no interruptions; synthesized 5' to 3' toward the replication fork

ligase: an enzyme that catalyzes the formation of a phosphodiester bond between adjacent 3'-OH and 5'-P atoms in DNA

linkage: the greater association in inheritance of two or more nonallelic genes than is to be expected from independent assortment; genes are linked because they reside on the same chromosome

locus: (plural: loci) the position that a gene occupies in a chromosome or within a segment of genomic DNA

LOD score: a technique for determining the most likely recombination frequency between two loci from pedigree analysis

Lyon hypothesis: the hypothesis that dosage compensation in mammals is accomplished by the random inactivation of one of the two X chromosomes in the somatic cells of females

map distance: the distance between genes expressed as map units or centiMorgans (cM)

meiosis: the nuclear process in diploid eukaryotes that results in gametes or spores with only one member of each original homologous pair of chromosomes per nucleus

merodiploid/merozygote: a partially diploid bacterial zygote containing an exogenotic chromosomal fragment donated by the F+ mate; the exogenote may also be introduced during transduction or sexduction

migration: in population genetics, the movement of individuals between different populations of a species, resulting in gene flow

mimicry: the similarity in appearance of one species of animal to another that affords one or both protection; mimic: the organism that imitates the phenotype of another species

mitosis: the nuclear division producing two daughter nuclei identical to the original nucleus; divided into four stages of prophase, metaphase, anaphase, and telophase

model: the organism whose phenotype is imitated by a mimic

monocistronic: coding for a single polypeptide chain; typical of eukaryotic cells

monosomic: having only one chromosome of a homologous chromosome

mRNA: messenger RNA; an RNA molecule that functions during translation to specify the sequence of amino acids in a nascent polypeptide

monozygotic twins: result from a separation of a fertilized egg; genetically identical

mutation: the process by which a gene undergoes structural changes

neo-Darwinism: the post-Darwinian concept that species evolve by the natural selection of adaptive phenotypes caused by mutant genes

non-coding strand: the DNA strand that serves as the actual template for transcription

nondisjunction: the failure of homologous chromosomes in meiosis I or sister chromatids in meiosis II to separate properly and to move to opposite poles; results in one daughter cell receiving both and the other daughter receiving none of the chromosomes in question

non-parental: see recombinant

non-recombinant: in mapping studies, offspring that have alleles arranged as in the original parents

nonsense codon: a ribonucleotide triplet signaling the termination of the translation of a protein chain

nucleolar organizer: the chromosomal region around which the nucleolus forms; site of tandem repeats of the major ribosomal RNA gene

nucleoside: a purine or pyrimidine base attached to ribose or deoxyribose

nucleotide: one of the monomeric units from which DNA or RNA polymers are constructed, consisting of a purine or pyrimidine base, a pentose, and a phosphoric acid group

Okazaki fragment: the short pieces of replicated DNA along the lagging strand that are later rejoined by DNA ligase

operator: a chromosomal region capable of interacting with a specific repressor, controlling the functioning of adjacent cistrons

operon: a unit consisting of one or more cistrons that function coordinately under the control of an operator gene

ordered spores: a linear sequence of four haploid meiotic spores (or pairs of spores produced by a post-meiotic division) within a fungi ascus; this arrangement allows identification of chromatids participating in crossover events

outbreeding: the crossing of genetically unrelated plants or animals

paracentric inversion: an inversion that excludes the centromere

parasexual: an offspring formed from more than a single parent, bypassing standard meiosis and fertilization; often occurs as a result of the fusion of two genetically unlike cells or nuclei

parental: see non-recombinant

parthenogenetic: the ability to reproduce offspring without fertilization of the egg

path diagram: a modified pedigree showing only the direct line of descent from common ancestors

pedigree: a diagram setting forth the ancestral history or genealogical register; may be used to determine the inheritance pattern of a particular trait

penetrance: the proportion of individuals of a specified genotype that show the expected phenotype under a defined set of environmental conditions

peptidyl transferase: an enzyme that catalyzes the transfer of the bond between tRNA and the amino acid to a new bond between amino acids

pericentric inversion: an inversion that includes the centromere

phenotype: the observable properties of an organism, produced by the genotype in conjunction with the environment

phenylketonuria (PKU): a hereditary disorder of amino acid metabolism in humans, inherited as an autosomal recessive

pleiotropy: the phenomenon where a single gene is responsible for a number of distinct and seemingly unrelated phenotypic effects

polycistronic: coding for two or more proteins

polygene: one of a group of genes that together control a quantitative character

polymer: a macromolecule composed of a covalently bonded collection of repeating subunits or monomers linked together during a repetitive series of similar chemical reactions

polymorphic: having two or more genetically different classes in the same interbreeding population

polyploidy: having more than two sets of chromosomes

polytene chromosome: a giant cablelike chromosome consisting of many identical chromatids lying in parallel

population: a geographically defined group of specific organisms sharing a common gene pool

position effect: the change in the expression of a gene accompanying a change in the position of the gene with respect to neighboring genes; the change in position may result from crossing over or from a chromosomal aberration

Pribnow box: a segment upstream from the start-point of prokaryotic structural genes to which the sigma subunit of the RNA polymerase binds; the nucleotides most commonly found are TATAAT

probability: the long-term frequency of an event relative to all alternative events, and usually expressed as a decimal fraction

product rule: the rule that states that the probability of the occurrence of independent events is the product of their separate probabilities

prokaryote: microorganisms that lack a membrane-bound nucleus containing chromosomes; other organelles are also absent

promoter: a region on a DNA molecule to which an RNA polymerase binds and initiates transcription

protein: a molecule composed of one or more polypeptide chains, each composed of a linear chain of amino acids covalently linked by peptide bonds

prototroph: an organism that is capable of growing on a defined minimal medium; often this is usually regarded as the wildtype strain

P site: holds the tRNA molecule that is attached to the growing end of the nascent polypeptide

Punnett square: the checkerboard method commonly used to determine the types of zygotes produced by a fusion of gametes from the parents; the results allow the computation of genotypic and phenotypic ratios

random mating: a population mating system in which every male gamete has an equal opportunity to join in fertilization with every female gamete, including those gametes derived from the same individuals

recessive trait: a trait controlled by an allele that does not express itself in the heterozygous condition

reciprocal cross: a cross with the phenotype of each sex reversed as compared with the original cross; made to test the role of parental sex on inheritance patterns

recombinant: the new individuals arising as a result of recombination

recombination: the occurrence of progeny with combinations of genes other than those that occurred in the parents, due to independent assortment or crossing over

regulator gene: a gene whose primary function is to control the rate of synthesis of the products of other distant genes

release factor: specific proteins that read termination codons and cause the release of the finished polypeptide

replication: a duplication process requiring copying from a template

replicon: a genetic element that behaves as an autonomous unit during DNA replication; contains a segment to which a specific RNA polymerase binds and a replicator locus at which DNA replication commences

repressible system: a regulatory system in which the product of a regulator gene blocks transcription of the operon only if it first reacts with an effector molecule; thus, transcription only occurs in the absence of the effector

repressor: a protein synthesized by a regulator gene that binds to an operator locus and blocks transcription of that operon

reverse transcriptase: an enzyme that synthesizes a single strand of DNA using RNA molecules as templates; occur in oncogenic RNA viruses

ribosome: an organelle that is the site of translation

RNA: ribonucleic acid; any of a family of polynucleotides characterized by their component sugar ribose and one of their pyrimidines; single-stranded and have lower molecular weight than DNA

RNA polymerase: an enzyme that transcribes an RNA molecule from the antisense strand of a DNA molecule

rRNA: ribosomal RNA; the RNA subunits that, together, compose a ribosome

rule of independent assortment: Mendel’s second rule, describing the independent segregation of alleles at different loci; “The alleles of one gene can segregate independently of the alleles of other genes.”

rule of segregation: Mendel’s first principle describing how genes are passed from one generation to the next; “A gamete receives only one allele from the pair of alleles possessed by an organism; fertilization (the union of two gametes) reestablishes the double number.”

sampling distribution: the distribution of frequencies with which various possible events could occur or a probability distribution defined by a particular mathematical expression

selection: the process in nature whereby one genotype leaves more offspring than another genotype because of superior life history attributes such as survival or fecundity

selection differential: the difference between the average value of a quantitative character in the whole population and the average value of those selected to be parents of the next generation

semi-conservative replication: the method of replication of DNA in which the molecule divides longitudinally, each half being conserved and acting as a template for the formation of a new strand

sex chromosome: heteromorphic chromosomes whose distribution in a zygote determines the sex of the organism

sexduction: the process whereby a fragment of genetic material from one bacterium is carried with the sex factor F to a second bacterium

sex-influenced trait: a phenotype that is conditioned by the sex of the individual; a gene may be dominant in males and recessive in females, or vice versa; the trait may be expressed only to a lesser degree in one sex

sex-limited trait: a phenotype expressed in only one sex, although it may be due to a sex-linked or autosomal gene

sex-linked inheritance: a special inheritance pattern for genes located on the X chromosome; the trait in question may be observed only in heterogametic individuals, and much less frequently in homogametic individuals

sexual selection: a theory that in certain species there occurs a struggle between males for mated and that characteristics enhancing the success of those bearing them would have value and be perpetuated irrespective of their general value in the struggle for existence

sigma factor: a polypeptide subunit of the RNA polymerase of E. coli; serves to recognize specific binding sites on DNA molecules for initiation of RNA transcription

single-stranded binding protein: a protein that binds to the single-stranded DNA generated when a helicase opens the double helix; this stabilizes the molecule and prevents reannealing or formation of intrastrand hydrogen bonds

species: a group of organisms capable of interbreeding to produce fertile offspring

spindle fibers: a collection of microtubules responsible for the movement of eukaryotic chromosomes during mitosis and meiosis

splicesome: the organelle in which the excision and splicing reactions that remove introns from premessenger RNAs occur

spontaneous reversion: the naturally occurring reverse of a mutation

stabilizing selection: the removal of those alleles that produce deviations from the average population phenotype by selection against all deviant individuals

start codon: a group of three adjacent ribonucleotides (AUG) in an mRNA that initiates polypeptide formation

sum rule: the rule that states that the probability of the occurrence of mutually exclusive events is the sum of the probabilities of the individual events

supercoiled: the coiling of a covalently closed circular duplex DNA molecule upon itself so that it crosses its own axis

supergene: a chromosomal segment protected from crossing over and so transmitted from generation to generation as if it were a single recon

supernatant: the fluid lying above a precipitate in a centrifuge following the centrifugation of a suspension

Svedberg unit: the rate at which a given solute molecule suspended in a less dense solvent sediments in a field of centrifugal force

synaptonemal complex: a proteinaceous complex that mediates synapsis during zygote stage and then disintegrates

tandem repeat: an aberration in which two identical chromosomal segments lie one behind the other

TATA box: a segment from the startpoint of eukaryotic structural genes to which RNA polymerase binds; the nucleotides most commonly found are TATAAAA

test cross: a mating between an individual of unknown genotype with an individual known to carry only the recessive alleles of the genes in question

testis-determining factor: general term for the gene determining maleness in the human being

tetrad: four homologous chromatids (two in each chromosome of a bivalent) synapsed during first meiotic prophase and metaphase

three-point cross: a series of crosses designed to determine the order of three, nonallelic, linked genes upon a single chromosome on the basis of their crossover behavior

topoisomerase: an enzyme that can unwind the supercoiling of a DNA helix

trans configuration: the situation in which the mutant allele of one gene and the wildtype allele of another gene are located on the same homologue; the two mutant alleles of the two different genes are located on different chromosomes of a homologous pair

transcription: the formation of an RNA molecule upon a DNA template by complementary base pairing; mediated by RNA polymerase

transduction: the transfer of bacterial genetic material from one bacterium to another using a phage as a vector

transformation: the phenomenon by which genes are transmitted from one bacterial strain to another in the form of soluble fragments of DNA that may originate from live or dead cells; once inside, a fragment usually replaces, by recombination, a short section of the DNA of the receptor cell that contains a zone of homology

translation: the formation of a protein directed by a specific messenger RNA molecule

translocation: a chromosome aberration which results in a change in position of a chromosomal segment within the genome, but does not change the total number of genes present

trisomic: a diploid organism that possesses one extra copy of a homologous pair of chromosomes

tRNA: transfer RNA; an RNA molecule that transfers an amino acid to a growing polypeptide chain during translation

virulent: possessing the ability to produce disease

Waring Blender: an electric kitchen appliance used to homogenize mixtures, but used in the laboratory to generate the shearing forces required to detach conjugating bacteria, to strip bacteriophages from host cells, to homogenize tissue samples, etc.

wobble theory: a hypothesis developed to explain how one tRNA may recognize two codons; the third base in the anticodon may pair with a variety of bases occupying the third position of a codon

Y-junction: the point at which a DNA molecule is being replicated; the two template strands separate, forming the arms, and the unreplicated double-stranded DNA forms the base of the Y

zygotic selection: the forces acting to cause differential mortality of an organism at any stage (other than gametes) in its life cycle

Last updated on 3 July 1997.
Provide comments to Dwight Moore at
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