Chiasma (pl. chiasmata) is a site at which two homologous chromosomes appear to have exchanged material during meiosis.
Chromatids are the copies of a chromosome produced by replication. The name is usually used to describe them in the period before they separate at the subsequent cell division.
Chromatin is the complex of DNA and protein in the nucleus of the interphase cell. Individual chromosomes cannot be distinguished in it .It was originally recognized by its reaction with stains specific for DNA.
Chromocenter is an aggregate of heterochromatin from different chromosomes.
Chromomeres are densely staining granules visible in chromosomes under certain conditions, especially early in meiosis, when a chromosome may appear to consist of a series of chromomeres.
Chromosome is a discrete unit of the genome carrying many genes. Each chromosome counsists of a very long molecule of duplex DNA and an approximately equal mass of proteins. It is visible as a morphological entity only during cell division.
Chromosome walking describes the sequential isolation of clones carrying overlapping sequences of DNA, allowing large regions of the chromosome to be spanned. Walking is often performed in order to reach a particular locus of interest.
cis-acting locus affects the activity only of DNA sequences on its own molecule of DNA; this property usually implies that the locus does not code for protein.
cis-acting protein has the exceptional property of acting only on the molecule of DNA from which it was expressed.
cis configuration describes two sites on the same molecule of DNA.
cis/trans test assays the effect of relative configuration on expression of two mutations. In a double heterozygote, two mutations in the same gene show mutant phenotype in trans configuration, wild-type in cis configuration.
Cistron is the geneti unit defined by the cis/trans test; equivalent to gene ib comprising a unit of DNA representing a protein.
Class switching is a change in the expression of the c cregion of an immunoglobulin heavy chain during lymphocyte differentiation.
Clone describes a large number of cells or molecules identical with a single ancestral cell or molecule.
Cloning vector is a plasmid or phage that is used to ‘carry’ inserted foreign DNA for the purposes of producing more material or a protein product.
Closed reading frame contains termination codons that prevent its translation into protein.
Coated vesicles are vesicles whose membrane has on its surface a layer of the protein clathrin.
Coconversion is the simultaneous correction of two sites during gene conversion.
Coding strand of DNA has the same sequence as mRNA.
Codominant alleles both contribute to the phenotype; neither is dominant over the other.
Coevolution —see concerted evolution.
Cognate tRNAs are those recognized by a particular aminoacy-tRNA synthetase.
Coointegrate structure is produced by fusion of two replicons, one originally possessing a transposon, the other lacking it; the cointegrate has copies of the transposon present at both junctions of the replicons, oriented as directrepeats.
Cold-sensitive mutant is defective at low temperature but functional at normal temlperature.
Colony hybridization is a technique for using in situ hybridization to identify bacteria carrying chimeric vectors whose inserted DNA is homologous with some particular sequence.
Compatibility group of plasmids contains members unable to coexist in the same bacterial cell.
Complementation refers to the ability of independent (nonallelic)genes to provide diffusible products that produce wild phenotype when two mutants are tested in trans configuration in a heterozygote.
In vitro complementation assay consists of identifying a component of a wid-type cell that can confer activity on an extract prepared from a mutant cell. The assay identifies the component rendered inactive by the mutation.
Complementation group is a series of mutations unable to complement when tested in pairwise combinations in trans; defines a genetic unit (the cistron) that might better be called a noncomplex mentation group.
Complex locus (of D. melanogaster) has genetic properties inconsistent with the function of a gene representing a single protein. Complex loci are usually very large (>100kb) at the molecular level.
Complexity is the total length of different sequences of DNA present in a given preparation.
Compostie transposons have a central region flanked on each side by insertion sequences, either or both of which may enable the entire element to transpose.
Concatemer of DNA consists of a series of unit genomes repeated in tandem.
Concatenated circles of DNA are interlocked like rings one a chain.
Concerted evolution describes the ability of two related genes to evolve together as though constituting a single locus.
Condensation reaction is one in which a covalent bond is formed with loss of a water molecule, as in the addition of an amino acid to a polypeptide chain.
Conditional lethal mlutations kill a cell or virus under certain (nonpermissive) conditions, but allow it to survive under other (permissive) conditions.
Conjugation describes ‘mathing’ between two bacterial cells, when (part of ) the chromosome is transferred from one to the other.
Consensus sequence is an idealized sequence in which each position represents the base most often found when many actual sequences are compared.
Conservative recombination involves breakage and reunion of preexisting strands of DNA without any synthesis of new stretches of DNA.
Conservative transposition refers to the movement of large elements, originally classified as transposons, but now considered to be episomes. The mechanism of movement resembles that of phage lambda.
Constant regions of immunoglobulins are coded by C genes and are the parts of the chain that vary least. Those of heavy chains identify the type of immunoglobulin.
Constitutive genes are expressed as a function of the interaction of RNA polymerase with the promoter, without additional regulation; sometimes also called household genes in the context of describing functions expressed in all cells at a low level.
Constitutive heterochromatin describes the inert state of permanently nonexpressed sequences, usually satellite DNA.
Constitutive mutations cause genes that usually are regulated to be expressed without regulation.
Contractile ring is a ring of actin filaments that forms around the equator at the end of mitosis and is responsible for pinching the daughter cells apart.
Controlling elements of maize are transposable units originally identified solely by their genetic properties. They may be autonomous (able to transpose independently) or nonautonomous (able to element).
Coordinate regulation refers to the common control of a group of genes.
Cordycepin is 3’ deoxyadenosine, an inhibitor of polyadenylation of RNA.
Core DNA is the 14.6 bp of DNA contained on a core particle.
Core particle is a digestion product of the nucleosome that retains the histone octamer and has 14.6 bp of DNA; its structure appears similar to that of the nucleosome itself.
Corepressor is a small molecule that triggers repression of transcription by binding to a regulator protein.
Cosmids are plasmids into which phage lambda cos sites have been inserted; as a result, the plasmid DNA can be packaged in vitro in the phage coat.
Cot is the product of DNA concentration and time of incubation in a reassociation reaction.
Cot  is the Cot required to proceed to half completion of the reaction; it is directly proportional to the unique length of reassociating DNA.
Cotransfection is the simultaneous transfection of two markers.
Crossing-over describes the reciprocal exchange of material between chromosomes that occurs during meiosis and is responsible for genetic recombination.
Crossover fixation refers to a possible consequence of unequal crossing-over that allows a mutation in one member of a tandem cluster to spread through the whole cluster (or to be eliminated).
Cruciform is the structure produced at inverted repeats of DNA if the repeated sequence pairs with its complement on the same strand (instead of with its regular partner in the other strand of the duplex).
Cryptic satellite is a satellite DNA sequence not identified as such by a separate peak on a density gradient; that is, it remains present in main-band DNA.
ctDNA is chloroplast DNA.
Cyclic AMP (cAMP) is a molecule of AMP in which the phosphate group is joined to both the 3’ and 5’ positions of the ribose; its binding activates the CAP, a postive regulator of prokaryotic transcription.
Cyclins are proteins that accumulate continuously throughout the cell cycle and are then destroyed by proteolysis during mitosis. (see also MPF).
Cytokinesis is the final process involved in separation and movement apart of daughter cells at the end of mitosis.
Cytological hybridization—see in situ hybridization.
Cytoplasm describes the material between the plasma membrane and the nucleus.
Cytoplasmic inheritance is a property of genes located in mitochondria or chloroplasts (or possibly other extranuclear organelles).
Cytoplasmic protein synthesis is the ranslation of mRNAs representing nuclear genes; it occurs via ribosomes attached to the cytoskeleton.
Cytoskeleton consists of networks of fibers in the cytoplasm of the eukaryotic cell.
Cytosol describes the general volume of cytoplasm in which organelles ( such as the mitochondria ) are located.