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Modern Genetic Analysis Glossary
C
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.
cancer The class of disease characterized by rapid and uncontrolled proliferation of cells within a tissue of a multitissued eukaryote. Cancers are generally thought to be genetic diseases of somatic cells, arising through sequential mutations that create oncogenes and inactivate tumor-suppressor genes.
candidate gene A sequenced gene of previously unknown function that, because of its chromosomal position or some other property, becomes a candidate for a particular function such as disease determination.
cap A 7-methylguanosine molecule added to the 5 end of pre-mRNA.
carbon source A nutrient (such as sugar) that provides carbon "skeletons" needed in an organism's synthesis of organic molecules.
carcinogen A substance that causes cancer.
cardinal gene Those pattern-formation genes in Drosophila that are the zygotically acting genes directly responding to the gradients of the anteriorposterior and dorsalventral positional information created by the maternally expressed pattern-formation genes.
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 A / a is a carrier of a if there is complete dominance of A over a.
caspase A member of a family of related proteases that take part in initiating and carrying out the cell death response.
cassette model A model to explain mating-type interconversion in yeast. Information for both a and a 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 unites with cAMP at low glucose concentrations and binds to the lac promoter to facilitate RNA polymerase action.
catabolite repression The inactivation of an operon caused by the presence of large amounts of the metabolic end product of the operon.
cation A positively charged ion (such as K+).
CDK See cyclin-dependent protein kinase.
cDNA See complementary DNA.
cDNA library A library composed of cDNAs, not necessarily representing all mRNAs.
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 set of events that take place in the divisions of mitotic cells. The cell cycle oscillates between mitosis (M phase) and interphase. Interphase can be subdivided in order into G1, S phase, and G2. DNA synthesis occurs during S phase. The length of the cell cycle is regulated through a special option in G1, in which G1 cells can enter a resting phase called G0.
cell division The process by which two cells are formed from one.
cell fate The ultimate differentiated state to which a cell has become committed.
cell lineage A pedigree of cells related through asexual division.
cellular blastoderm The stage of blastoderm in insects after the nuclei have each been packaged in an individual cellular membrane.
centimorgan (cM) See map unit.
central dogma The hypothesis that information flows only from DNA to RNA to protein; although some exceptions are now known, the rule is generally valid.
centromere A specialized region of DNA on each eukaryotic chromosome that acts as a site for binding of the kinetochore proteins.
character Some attribute of individuals within a species for which various heritable differences can be defined.
character difference Alternative forms of the same attribute within a species.
chase See pulse-chase experiment.
checkpoints Stages of the cell cycle at which the completion of certain events of the cell cycle, such as chromosome replication, must have been successfully completed in order for the cell cycle to progress to the next stage.
chi-square c 2) test A statistical test used to determine the probability of obtaining observed proportions by chance, under a specific hypothesis.
chiasma (chiasmata) A cross-shaped structure commonly observed between nonsister chromatids in meiosis; the site of crossing-over.
chimera See mosaic.
chimeric DNA See recombinant DNA.
chloroplast A chlorophyll-containing organelle in plants that is the site of photosynthesis.
chorionic villus sampling See CVS.
chromatid One of the two side-by-side replicas produced by chromosome division.
chromatid conversion A type of 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 inference 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.
chromocenter The point at which the polytene chromosomes appears to be attached together.
chromomere A small beadlike structure visible on a chromosome during prophase of meiosis and mitosis.
chromosome A linear end-to-end arrangement of genes and other DNA, sometimes with associated protein and RNA.
chromosome aberration Any type of change in the chromosome structure or number.
chromosome loss Failure of a chromosome to become incorporated into a daughter nucleus at cell division.
chromosome map See linkage map.
chromosome mutation Any type of change in the chromosome structure or number.
chromosome puff A swelling at a site along the length of a polytene chromosome; the site of active transcription.
chromosome rearrangement A chromosome mutation in which chromosome parts are in new juxtaposition.
chromosome set The group of different chromosomes that carries the basic set of genetic information of a particular species.
chromosome theory of inheritance 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 method for the dissection of large segments of DNA, in which a cloned segment of DNA, usually eukaryotic, is used to screen recombinant DNA clones from the same genome bank for other clones containing neighboring sequences.
cis-acting element A site on a DNA (or RNA) molecule that functions as a binding site for a sequence-specific DNA (or RNA) binding protein. The term "cis-acting" indicates that protein binding to this site affects only nearby DNA (or RNA) sequences on the same molecule.
cis conformation In a heterozygote involving two mutant sites within a gene or within a gene cluster, the arrangement 11 / a1a2.
cis dominance The ability of a gene to affect genes next to it on the same chromosome.
cis-regulatory element See cis-acting element.
cis-trans test A test to determine whether two mutant sites of a gene are in the same functional unit or gene.
cistron 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 function RNA molecule such as tRNA or rRNA).
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." (3) See DNA clone.
cM (centimorgan) See map unit.
code dictionary A listing of the 64 possible codons and their translational meanings (the corresponding amino acids).
codominance The situation in which a heterozygote shows the phenotypic effects of both alelles equally.
codon A section of DNA (three nucleotide pairs in length) that encodes a single amino acid.
coefficient of coincidence The ratio of the observed number of double recombinants to the expected number.
cohesive ends Ends of DNA that are cut in a staggered pattern and can then hydrogen-bond with complementary base sequences from other similarly formed ends.
cointegrate The product of the fusion of two circular elements to form a single, larger circle.
colinearity The correspondence between the location of a mutant site within a gene and the location of an amino acid substitution within the polypeptide translated from that gene.
colony A visible clone of cells.
compartmentalization The existence of boundaries within an organism beyond which a specific clone of cells will never extend during development.
competent Able to take up exogenous DNA and thereby be transformed.
complementary DNA (cDNA) Synthetic DNA transcribed from a specific RNA through the action of the enzyme reverse transcriptase.
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.
complementation test See cis-trans test.
complex trait Discontinuous variant whose inheritance can be explained by the interaction of several genes plus the environment.
conditional mutation A mutation that has the wild-type phenotype under certain (permissive) environmental conditions and a mutant phenotype under other (restrictive) conditions.
conjugation The union of two bacterial cells, during which chromosomal material is transferred from the donor to the recipient cell.
conjugation tube See pilus.
conservative replication A disproved model of DNA synthesis suggesting that one-half of the daughter DNA molecules should have both strands composed of newly polymerized nucleotides.
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 (in reference to gene control).
constitutive expression Constant expression of a gene product, regardless of environmental conditions.
constitutive heterochromatin Specific regions of hetero-chromatin always present and in both homologs of a chromosome.
contig A set of ordered overlapping clones that constitute a chromosomal region or a genome.
continuous variation Variation showing an unbroken range of phenotypic values.
controlling element A mobile genetic element capable of producing an unstable mutant target gene; two types exist, the regulator and the receptor elements.
correction The production (possibly by excision and repair) of a properly paired nucleotide pair from a sequence of hybrid DNA that contains an illegitimate pair.
correlation coefficient A statistical measure of the extent to which variations in one variable are related to variations in another.
cosegregation Parallel inheritance of two genes due to their close linkage on a chromosome.
cosmid A cloning vector that can replicate autonomously like a plasmid and be packaged into a phage.
cotransduction The simultaneous transduction of two bacterial marker genes.
cotransformation The simultaneous transformation of two bacterial marker genes.
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

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