| C |
| Cytosine or cytidine. |
| callus |
| An undifferentiated clone of plant cells.
|
| cAMP (cyclic adenosine
monophosphate) |
| A molecule that plays a key role in the
regulation of various processes within the cell. |
| canalized character |
| A character whose phenotype is kept within
narrow boundaries even in the presence of disturbing environments
or mutations. |
| cancer |
| A syndrome that involves the uncontrolled
and abnormal division of eukaryotic cells. An informal term for
a diverse class of diseases marked by abnormal cell proliferation.
|
| cancer-family syndrome
|
| pedigree in which unusually large numbers
of blood relatives develop certain kinds of cancers. |
| capsid |
| The protein shell of a virus. |
| capsomere |
| Protein clusters making up discrete subunits
of a viral protein shell. |
| carbon source |
| A nutrient (such as sugar) that provides
carbon skeletons needed for synthesis of new organic molecules (anabolism).
|
| carcinogen |
| An agent (chemical or radiation) that causes
cancer. |
| carcinoma |
| tumour arising from epithelial tissue (eg
glands; breast; skin; linings of the urogenital, intestinal and
respiratory systems). |
| carrier |
| An individual who possesses a mutant allele
but does not express it in the phenotype because of a dominant allelic
partner; thus, an individual of genotype Aa is a carrier of a, if
there is complete dominance of A over a. |
| cassette mechanism |
| The mechanism by which homothallic yeast
cells alternate mating types, involves two silent transposons (cassettes)
and a region where these cassettes can be expressed (cassette player).
|
| cassette model |
| A model to explain mating-type switching
in yeast. Information for both a and alpha mating types is assumed
to be present as silent cassettes ; a copy of either type of cassette
may be transposed to the mating-type locus, where it is played (transcribed).
|
| catabolite activator
protein (CAP) |
| A protein that when bound with cyclic AMP
can attach to sites on sugar-metabolizing operons to enhance transcription
of these operons. |
| catabolite repression
|
| Repression (inactivation) of certain sugar-metabolizing
operons (eg lac) in favour of glucose utilization when glucose is
the predominant carbon source in the environment of the cell. |
| catalyst |
| A substance that increases the rate of a
chemical reaction without itself being permanently changed. |
| CCAAT box |
| An invariant DNA sequence at about minus
70 base pairs from the origin of transcription in many eukaryotic
promoters. |
| cDNA |
| See complementary DNA. |
| cDNA library |
| A pool of complementary DNA clones produced
by cDNA cloning of total messenger RNA from a single source (cell
type, tissue, embryo). |
| cell autonomous |
| A genetic trait in multicellular organisms
in which only genotypically mutant cells exhibit the mutant phenotype.
Conversely, a nonautonomous trait is one in which genotypically
mutant cells cause other cells (regardless of their genotype) to
exhibit a mutant phenotype. |
| cell cycle |
| The cycle of cell growth, replication of
the genetic material and nuclear and cytoplasmic division. |
| cell division |
| The process by which two cells are formed
from one. See meiosis and mitosis |
| cell fate |
| The ultimate differentiated state to which
a cell has become committed. |
| cell lineage |
| A pedigree of cells related through asexual
division. |
| cell-free system |
| A mixture of cytoplasmic and/or nuclear
components from cells and used for in vitro protein synthesis or
transcription or DNA replication or other purposes. |
| cellular blastoderm |
| The stage of the blastoderm, initially a
syncytium, in insects after the nuclei have each been separately
packaged into a cell membrane. |
| centimorgan (cm) |
| A chromosome mapping unit. One centimorgan
equals 1% recombinant offspring. |
| central dogma |
| The original postulate that genetic information
can be transferred only from nucleic acid to nucleic acid and from
nucleic acid to protein, that is from DNA to DNA from DNA to RNA
and from RNA to protein (although information transfer from RNA
to DNA was not excluded and is now known to occur [reverse transcription]).
Transfer of genetic information from protein to nucleic acid never
occurs. |
| centric fragment |
| A piece of chromosome containing a centromere.
|
| centriole |
| A short cylindrical organelle, found in
pairs arranged at right angles to each other at the centre of a
microtubule organizing centre (MTOC) or centrosome, found in eukaryotes
(except in higher plants). A centriole is similar in structure to
the basal body found at the base of eukaryotic cilia and flagella
and organises the axoneme, the bundle of microtubules and other
proteins forming the core of each cilium or flagellum. The centrosome
organizes formation of a spindle during mitosis or meiosis. |
| centromere |
| A kinetochore; the constricted region of
a nuclear chromosome, to which the spindle fibres attach during
division. |
| centromere marker |
| locus located close to a centromere. |
| centromeric fission |
| Creation of two chromosomes from one by
splitting the centromere. |
| centrosome |
| The primary microtubule organising center
(MTOC) of animal cells, that divides prior to cell division each
daughter MTOC acts as one pole of the spindle apparatus. The centrosome
usually contains a pair of centrioles. |
| chaperone |
| See molecular chaperone. |
| character |
| An attribute of individuals within a species
for which heritable differences can be defined. |
| character difference
|
| Alternative forms of the same attribute
within a species. |
| Chargaff's rule |
| Chargaff's observation that in the base
composition of DNA the quantity of adenine equaled the quantity
of thymine and the quantity of guanine equaled the quantity of cytosine.
|
| Charon phage |
| Phage lambda derivative used as vector in
DNA cloning. |
| chi-square distribution
|
| The sampling distribution of the chi-square
statistic. A family of curves whose shapes depend on degrees of
freedom. |
| chi-square test |
| A statistical test used to determine the
probability of obtaining the observed results by chance, under a
specific hypothesis. |
| chiasma (plural chiasmata)
|
| A cross-shaped structure commonly observed
between nonsister chromatids during meiosis; the site of crossing-over.
X-shaped configuration seen in tetrads during the latter stages
of prophase 1 of meiosis. They represent physical crossovers between
DNA molecules. |
| chimeric plasmid |
| Hybrid or genetically mixed plasmid used
in DNA cloning. |
| chloroplast |
| The organelle that carries out photosynthesis
and starch grain formation. A chlorophyll-containing organelle in
plants that is the site of photosynthesis. |
| chromatid |
| One of the two side by side replicas produced
by chromosome replication in mitosis or meiosis. Subunit of a chromosome
after replication and prior to anaphase of meiosis II or mitosis.
At anaphase of meiosis II or mitosis when the centromeres divide
and the sister chromatids separate each chromatid becomes a chromosome.
|
| chromatid conversion
|
| Gene conversion that is inferred from the
existence of identical sister-spore pairs in a fungal octad that
shows a non-Mendelian allele ratio. |
| chromatid interference
|
| A situation in which the occurrence of a
crossover between any two nonsister chromatids can be shown to affect
the probability of those chromatids being involved in other crossovers
in the same meiosis. |
| chromatin |
| The substance of chromosomes; now known
to include DNA, chromosomal proteins, and chromosomal RNA. The nucleoprotein
material of the eukaryotic chromosome. |
| chromocenter |
| The point at which polytene chromosomes
appear to be attached together. |
| chromomere |
| A small beadlike structure visible on a
chromosome during prophase of meiosis and mitosis. Dark regions
of chromatin condensation in eukaryotic chromosomes at meiosis or
mitosis. |
| chromosome |
| A linear end-to-end arrangement of genes
and other DNA, sometimes with associated protein and RNA. The form
of the genetic material in viruses and cells. A circle of DNA in
prokaryotes; a DNA or an RNA molecule in viruses; a linear nucleoprotein
complex in eukaryotes. |
| chromosome aberration
|
| Any type of change in the chromosome structure
or number. |
| chromosome jumping |
| A technique of isolating clones from a genomic
library that are not contiguous by skipping a region between known
points on the chromosome. Done usually to bypass regions that are
difficult or impossible to walk through or regions known not to
be of interest. |
| chromosome loss |
| Failure of a chromosome to become incorporated
into a daughter nucleus at cell division. |
| chromosome marker |
| Any distinct and heritable feature of chromosome
structure that can be used to follow (usually by microscopy) that
chromosome or chromosome region in breeding experiments. |
| chromosome map |
| See linkage map. |
| chromosome mutation |
| Any type of change in the chromosome structure
or number. |
| chromosome painting |
| The use of fluorescent-tagged chromosome-specific
dispersed repeat DNA sequences to visualize specific chromosomes
or chromosome segments by in situ DNA hybridization and fluorescence
microscopy. |
| chromosome puff |
| A swelling at a site along the length of
a polytene chromosome; the site of active transcription. A diffuse
uncoiled region in a polytene chromosome where transcription is
actively taking place. |
| chromosome rearrangement
|
| A chromosome mutation involving new juxtapositions
of chromosome parts. |
| chromosome set |
| The group of different chromosomes that
carries the basic set of genetic information for a particular species.
|
| chromosome theory of
inheritance |
| The theory that chromosomes are linear sequences
of genes. The unifying theory stating that inheritance patterns
may be generally explained by assuming that genes are located in
specific sites on chromosomes. |
| chromosome walking |
| A technique which produces sets of overlapping
DNA clones for studying segments of DNA larger than can be cloned
individually. A method for the analysis of large regions of DNA,
in which a each end of a large single cloned DNA fragment is used
separately to screen recombinant DNA genome library for other clones
containing neighbouring sequences. |
| cis |
| Meaning on the near side of; refers to geometric
configurations of atoms or mutations on the same molecule or chromosome.
|
| cis conformation |
| In a heterozygote involving two mutant sites
(a,b) within a gene or within a gene cluster, the arrangement ab/AB.
|
| cis dominance |
| The ability of a gene to affect genes next
to it on the same chromosome. |
| cis-dominant |
| mutations (eg of an operator) that alter
the functioning of genes on that same piece of DNA. |
| cistron |
| Term coined by Benzer for the smallest genetic
unit that does NOT show genetic complementation when two different
mutations are in trans during a cis-trans complementation test;
but shows wild-type phenotype when the same mutations are in cis.
Synonymous with gene. Originally defined as a functional genetic
unit within which two mutations cannot complement. Now equated with
the term gene, as the region of DNA that encodes a single polypeptide
(or functional RNA molecule such as tRNA or rRNA). |
| cladogenesis |
| The evolutionary process whereby one species
splits into two or more species. See anagenesis. |
| ClB method |
| A technique devised by Muller to rapidly
screen fruit flies for recessive X chromosome lethal mutations.
The ClB chromosome carries a recessive lethal (l) a dominant marker
(B) and an inversion (crossover suppressor C). |
| clinal selection |
| Selection that changes gradually along a
geographic gradient. |
| clone |
| (1) A group of genetically identical cells
or individuals derived by asexual division from a common ancestor. |
| (2) (colloquial), An individual formed by
some asexual process so that it is genetically identical to its
parent. |
| coccus |
| A spherical bacterium. |
| code dictionary
|
| A listing of the 64 possible codons
and their translational meanings (the corresponding amino
acids). |
| coding strand |
| The DNA strand with the same sequence
as the transcribed mRNA (given U in RNA and T in DNA) and
containing the linear array of codons which interact with
anticodons of tRNA during translation to give the primary
sequence of a protein. Compare with anticoding strand. |
| codominance |
| The situation in which a heterozygote
shows the phenotypic effects of both alleles equally, (eg
blood group antigens). |
| codon |
| A section of DNA (three nucleotide
pairs in length) or RNA (three nucleotides in length) that
codes for a single amino acid. A sequence of three RNA or
DNA nucleotides that specifies (codes for) either an amino
acid or the termination of translation. |
| codon preference
|
| The idea that for amino acids with
several codons one or a few are preferred and are used disproportionately.
They would correspond with tRNAs that are abundant. |
| coefficient of
coincidence |
| In a three point cross the number
of observed double crossovers divided by the number expected
based on the observed occurrence of single crossovers. The
ratio of the observed number of double recombinants to the
expected number. |
| coefficient of
relationship (r) |
| The proportion of alleles held in
common by two related individuals. |
| cohesive end |
| A single-stranded end to a linear
duplex DNA molecule which can hydrogen-bond with a complementary
single-strand base sequence from the end of the same or another
DNA molecule. |
| cointegrate |
| A fusion of two elements. An intermediate
structure in replicative transposition. The product of the
fusion of two circular elements to form a single, larger circle.
|
| col plasmid |
| plasmid that produces an antibiotic
(colicin) used by the host to kill other strains of bacteria.
|
| colinearity |
| The one to one linear correspondence
between the order of codons in a coding sequence and the order
of amino acids in the protein encoded. A linear map of mutation
sites within a gene corresponds to the linear location of
amino acid substitutions within the polypeptide encoded by
that gene. |
| colony |
| A visible clone of cells. |
| common ancestry
|
| The state of two individuals when
they are blood relatives. When two parents have a common ancestor
their offspring will be inbred. |
| compartment |
| The existence of boundaries within
the organism beyond which a specific clone of cells will never
extend during development. |
| competence factor
|
| A surface protein that binds extracellular
DNA and enables the cell to be transformed. |
| competent |
| Able to take up exogenous DNA and
thereby be transformed. |
| complementarity
|
| The correspondence of DNA bases in
the double helix such that adenine in one strand is opposite
thymine in the other strand and cytosine in one strand is
opposite guanine in the other. This relationship explains
Chargaff's rule. |
| complementary DNA
(cDNA) |
| Synthetic DNA reverse transcribed
from a specific RNA through the action of the enzyme reverse
transcriptase. DNA synthesized by reverse transcriptase using
RNA as a template. |
| complementary RNA
(cRNA) |
| Synthetic RNA produced by transcription
from a specific DNA single stranded template. |
| complementation
|
| The production of a wild-type phenotype
when two different mutations are combined in a diploid or
a heterokaryon. The production of the wild-type phenotype
by a cell or an organism that contains two mutant genes. If
complementation occurs the mutations are almost certainly
non-allelic (ie in different genes). |
| complementation
group |
| A group of mutant genes which do not
complement each other. A cistron (determined by the cis-trans
complementation test). |
| complementation
test |
| A mating test to determine whether
two different recessive mutations (a1;a2) on opposite chromosomes
(trans, a1+/+a2) of a diploid or partial diploid will not
complement (ie have a mutant phenotype) each other; but the
same two recessive mutations on the same chromosome (cis,
a1a2/++) in a diploid or partial diploid show a wild-type
phenotype; a test for allelism. A test to determine whether
two mutant sites are in the same functional unit or gene.
|
| complete linkage
|
| The state in which two loci are so
close together that alleles of these loci are virtually never
separated by crossing over. |
| complete medium
|
| A culture medium that is enriched
to contain all of the growth requirements of a strain of organisms.
|
| component of fitness
|
| A particular aspect in the life cycle
of an organism upon which natural selection acts. |
| composite transposon
|
| A transposon constructed of two IS
(insertion sequence) elements flanking a control region that
frequently contains host genes. |
| concordance |
| The amount of similarity in phenotype
between individuals. |
| conditional mutation
|
| A mutation that has the wild-type
phenotype under certain (permissive) environmental conditions
and a mutant phenotype under other (restrictive) conditions.
|
| conditional-lethal
mutation |
| A mutation that is lethal under one
condition but not lethal under another condition. |
| confidence limits
|
| A statistical term for a pair of numbers
that predict the range of values within which a particular
parameter lies for a given level of confidence (probability).
|
| conjugation |
| A process whereby two cells come in
contact and exchange genetic material. In prokaryotes the
transfer is a one-way process. The union of two bacterial
cells, during which chromosomal material is transferred from
the donor to the recipient cell. Conjugation in Protozoa is
a two-way process, genetic material is passed between each
conjugant. |
| consanguineous
|
| Meaning between blood relatives ;
usually refers to inbreeding or incestuous matings. |
| consensus sequence
|
| A sequence of nucleotides or amino
acids in common between regions of homology in different but
related DNA or RNA or protein sequences. |
| 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. A disproved model of
DNA synthesis suggesting that one-half of the daughter DNA
molecules should have both strands composed of newly polymerized
nucleotides. |
| conserved sequence
|
| An invariant sequence found in different
DNA or RNA or protein sequences. |
| constant region
|
| A region of an antibody molecule that
is nearly identical with the corresponding regions of antibodies
of different specificities. |
| constitutive |
| Always expressed in an unregulated
fashion (when referring to gene control). |
| constitutive heterochromatin
|
| Heterochromatin that surrounds the
centromere. Specific regions of heterochromatin always present
and in both homologs of a chromosome. See satellite DNA. |
| constitutive mutation
|
| A mutation which causes transcription
to be no longer under regulatory control. |
| continuous replication
|
| The uninterrupted replication of DNA
in the 5' to 3' direction using a 3' to 5' template. |
| continuous variation
|
| Variation measured on a continuum
rather than in discrete units or categories (eg height in
human beings). |
| controlling element
|
| A term used by maize geneticists to
indicate a mobile genetic element capable of producing an
unstable mutant target gene; two types exist, the regulator
and the receptor elements. |
| copper fist |
| Configuration of a DNA-binding protein
that resembles a fist closed around a penny. In this case
the penny is copper ions; the knuckles of the fist of the
yeast ACE1 protein interact with the promoter of the metallothionein
gene, enhancing its transcription. |
| copy-choice hypothesis
|
| An incorrect hypothesis that stated
that recombination resulted from the switching of the DNA-replicating
enzyme from one DNA homologue to the other. |
| copy-choice model
|
| A model of the mechanism for crossing
over, suggesting that crossing over occurs during chromosome
division and can occur only between two supposedly new nonsister
chromatids; the experimental evidence does not support this
model. |
| corepressor |
| The metabolite that when bound to
the repressor (of a repressible operon) forms a functional
unit that can bind to its operator and block transcription.
|
| correction |
| The production (possibly by excision
and repair) of a properly paired nucleotide pair from a sequence
of hybrid DNA that contains a mismatched base pair. See mismatch
repair |
| correlation coefficient
|
| A statistic that gives a measure of
how closely two variables are related. A statistical measure
of the extent to which variations in one variable are related
to variations in another. |
| cosegregation |
| The tendency for closely linked genes
and genetic markers to segregate (be inherited) together.
|
| cosmid |
| A hybrid plasmid that contains cos
sites at each end. Cos sites are recognized during head filling
of lambda phages. Cosmids are useful for cloning large segments
of foreign DNA (up to 50 kb). |
| cotransduction
|
| The simultaneous transduction of two
or more genes. The simultaneous transduction of two bacterial
marker genes. |
| cotransformation
|
| The simultaneous transformation of
two bacterial marker genes. |
| coupling |
| Arrangement of wild-type and mutant
alleles at two linked loci in which both mutants are on the
same chromosome and both wild-type alleles on the homologue
(ab/AB). See repulsion |
| coupling conformation
|
| Linked heterozygous gene pairs in
the arrangement, AB/ab. |
| covariance |
| A statistical measure used in computing
the correlation coefficient between two variables; the covariance
is the mean of (x- x(bar))(y-y(bar)) over all pairs of values
for the variables x and y, where x(bar) is the mean of the
x values and y(bar) is the mean of the y values. A statistical
value measuring the simultaneous deviations of x and y variables
from their means. |
| cpDNA |
| Chloroplast DNA. |
| cri-du-chat syndrome
|
| A non-lethal human condition in infants
caused by deletion of part of one homologue of chromosome
5. |
| crisscross inheritance
|
| Transmission of a gene from male parent
to female child to male grandchild for example, X-linked inheritance.
|
| cross |
| The deliberate mating of two parental
types of organisms in genetic analysis. |
| crossbreed |
| Fertilization between separate individuals.
|
| crossing over |
| A process in which homologous chromosomes
exchange parts normally reciprocally but sometimes unequally.
The exchange of corresponding chromosome parts between homologues
by breakage and reunion of DNA molecules normally during prophase
I of meiosis but also occasionally during mitosis. |
| crossover suppression
|
| Reduction of crossing over within
an inversion loop in inversion heterozygotes due to physical
constraints during synapsis. Crossing over within an inversion
loop, when it does occur, leads to defective (deleted and
duplicated) crossover chromosomes and mortality of zygotes
carrying them. |
| cruciform configuration
|
| A region of DNA having a sequence
at one end repeated but inverted at the other end, so that
each strand may pair with itself to form a helix extending
sideways from the main helix. |
| cryptic coloration
|
| Coloration that allows an organism
to match its background and hence become less vulnerable to
predation or recognition by prey. |
| culture |
| Tissue or cells multiplying by asexual
division, grown for experimentation. |
| cyclic AMP (cAMP)
|
| A form of AMP (adenosine monophosphate)
used frequently as a second messenger in eukaryotics and in
catabolite repression in prokaryotes. |
| Cys |
| Cysteine (an amino acid). |
| cystic fibrosis
(CF) |
| A potentially lethal human disease
of secretory cells, showing excess lung mucus secretion, and
inherited as an autosomal recessive on chromosome 7. CF is
caused by mutations in a gene encoding the cystic fibrosis
membrane conductance regulator, a transmembrane protein involved
in ion transport. |
| cytidine |
| The nucleoside containing cytosine
as its base. |
| cytochrome |
| A class of protein, found in mitochondrial
membranes, whose main function is oxidative phosphorylation
of ADP to form ATP. |
| cytogenetics |
| The cytological approach to genetics,
mainly involving microscopic studies of chromosomes. |
| cytohet |
| A cell containing two genetically
distinct types of a specific organelle. |
| cytokinesis |
| The division of the cytoplasm of a
cell into two daughter cells. See karyokinesis. |
| cytoplasm |
| The material between the nuclear and
cell membranes; includes fluid (cytosol) organelles, and various
membranes. |
| cytoplasmic inheritance
|
| Inheritance via genes found in cytoplasmic
organelles. Extra-chromosomal inheritance controlled by non-nuclear
genomes. |
| cytosine |
| A pyrimidine base that pairs with
guanine. See pyrimidine. |
| cytosol |
| The fluid portion of the cytoplasm,
outside the organelles. |
| cytotoxic T lymphocyte
(Tc) |
| T lymphocyte responsible for attacking
cancerous host cells or cells infected with an invading bacterium
or virus. |
|
