cAMP (cyclic AMP)
Adenosine 3’, 5’ monophosphate; an intracellular regulatory molecule involved in controlling gene expression and some other processes in both prokaryotes and eukaryotes.
Cancer
Disease characterized by the uncontrolled and abnormal division of cells and by the spread of malignant tumor cells (metastasis) to disparate sites in the organism.
5’ capping
The addition of a methylated guanine nucleotide (a “cap”) to the 5’ end of a precursor mRNA (pre-mRNA) molecule in eukaryotes; the cap is retained on the mature mRNA molecule.
Carcinogen
Any physical or chemical agent that increases the frequency with which cells become cancerous.
Carrier
An individual who is heterozygous for a recessive mutation. A carrier usually does not exhibit the mutant phenotype.
Catabolite activator protein (CAP)
A regulatory protein that binds with cyclic AMP (cAMP) at low glucose concentrations, forming a complex that stimulates transcription of the lac operon and some other bacterial operons.
Catabolite repression
The inactivation of some inducible operons in the presence of glucose even though the operon’s inducer is present. Also called glucose effect.
cDNA
DNA copies made from RNA templates in a reaction catalyzed by the enzyme reverse transcriptase.
cDNA library
Collection of cloned complementary DNAs (cDNAs) produced from the entire mRNA population of a cell.
Cell cycle
The cyclical process of growth and cellular reproduction in unicellular and multicellular eukaryotes. The cycle includes nuclear division, or mitosis, and cell (cytoplasmic) division, or cytokinesis.
Cell division
A process whereby one cell divides to produce two cells.
CEN sequence
Nucleotide sequence of DNA in the centromere region of yeast chromosomes. Centromere sequences differ among species and between chromosomes in the same species.
Centimorgan (cM)
The unit of distance on a genetic map. Equivalent to map unit.
Centromere
The region of a chromosome containing DNA sequences to which mitotic and meiotic spindle fibres attach. Under the microscope a centromere is seen as a constriction in the chromosome. The centromere region of each chromosome is responsible for the accurate segregation of replicated chromosomes to the daughter cells during mitosis and meiosis.
Chain-terminating codon
One of three codons in mRNA for which no normal tRNA molecule exists and that signals the termination of polypeptide synthesis. .
Character
A characteristic that results from gene action and is transmitted from one generation to another. .
Charged tRNA
An enzyme that catalyzes the addition of a specific amino acid to the tRNA for that amino acid.
Charging
Addition of an amino acid to a tRNA that contains an anticodon for that amino acid. Also called aminoacylation. checkpoints, cell-cycle Stages in the cell cycle at which progression of a cell through the cycle is blocked if there is damage to the genome or the mitotic machinery.
Chiasma
(plural, chiasmata) A cross-shaped structure formed during crossing-over and visible during the diplonema stage of meiosis.
Chiasma interference
Phenomenon in which the presence of one crossover interferes with the formation of another crossover nearby. Mathematically defined as 1 minus the coefficient of coincidence.
Chi-square test
A statistical procedure that determines what constitutes a significant difference between observed results and results expected on the basis of a particular hypothesis; a goodness-of-fit test.
Chloroplasts
Triple-membraned, chlorophyll-containing organelles found in green plants in which photosynthesis occurs.
Chorionic villus sampling
A procedure in which a sample of chorionic villus tissue of a developing fetus is examined for chromosomal abnormalities.
Chromatid
One of the two visibly distinct replicated copies of each chromosome that becomes visible between early prophase and metaphase of mitosis and is joined to its sister chromatid at their centromeres.
Chromatin
The DNA–protein complex that constitutes eukaryotic chromosomes and can exist in various degrees of folding or compaction.
Chromatin remodelling
Alteration of the structure of chromatin in the vicinity of a core promoter in a way that stimulates or represses transcription initiation. Remodelling is carried out by enzymes catalyzing histone acetylation or deacetylation and by nucleosome remodelling complexes.
Chromosomal aberration
The variation from the wild-type condition in chromosome number or structure.
Chromosomal mutation
The variation from the wild-type condition in chromosome number or structure.
Chromosome
In eukaryotic cells, a linear structure composed of a single DNA molecule complexed with protein. Each eukaryotic species has a characteristic number of chromosomes in the nucleus of its cells. Most prokaryotic cells contain a single, usually circular chromosome.
Chromosome library
Collection of cloned DNA fragments produced from a particular chromosome (e.g., the human X chromosome).
Chromosome theory of inheritance
The theory that genes are located on chromosomes and that the transmission of chromosomes from one generation to the next accounts for the inheritance of hereditary traits.
Cis-dominant
Referring to a gene or DNA sequence that can control genes on the same DNA molecule but not on other DNA molecules.
Cis-trans test
See A test used to determine whether two independently isolated mutations that confer the same phenotype are located within the same gene or in two different genes.
Classical model
An early model for genetic variation that was based on the assumption that most natural populations had a wild-type allele with very few mutant alleles present.
Cline
A systematic change in allele frequencies within a continuous population distributed over a geographic region.
Clonal selection
A process whereby cells that express cellsurface antibodies specific for a particular antigen are stimulated to proliferate and secrete that antibody by exposure to that antigen.
Cloning
The production of many identical copies of a DNA molecule by replication in a suitable host; also called DNA cloning, gene cloning, and molecular cloning. (b) The generation of cells (or individuals) genetically identical to themselves and to their parent.
Cloning vector
A double-stranded DNA molecule that is able to replicate autonomously in a host cell and into which a DNA fragment (or fragments) can be inserted to form a recombinant DNA molecule for cloning.
Coactivator
In eukaryotes, a large multiprotein complex that interacts with activators bound at enhancers, general transcription factors bound near the promoter, and RNA polymerase II. These interactions help stimulate transcription of regulated genes.
Coding sequence
The part of an mRNA molecule that specifies the amino acid sequence of a polypeptide during translation.
Codominance
The condition in which an individual heterozygous for a gene exhibits the phenotypes of both homozygotes.
Codon
A group of three adjacent nucleotides in an mRNA molecule that specifies either one amino acid in a polypeptide chain or the termination of polypeptide synthesis.
Codon usage bias
A disproportionate use of one or a few synonymous codons within a codon family for a particular gene or across a genome.
Coefficient of coincidence
A measure of the extent of chiasma interference throughout a genetic map; ratio of the observed to the expected frequency of double crossovers.
Combinatorial gene regulation
In eukaryotes, control of transcription by the combined action of several activators and repressors, which bind to particular gene regulatory sequences.
Comparative genomics
Comparison of the nucleotide sequences of entire genomes of different species, with the Glossary 3 goal of understanding the functions and evolution of genes. Such comparisons can identify which genome regions are evolutionarily conserved and likely to represent functional genes.
Complementary base pairs
The specific A-T and G-C base pairs in double-stranded DNA. The bases are held together by hydrogen bonds between the purine and pyrimidine base in each pair.
Complementary DNA
DNA copies made from RNA templates in a reaction catalyzed by the enzyme reverse transcriptase.
Complementation test
A test used to determine whether two independently isolated mutations that confer the same phenotype are located within the same gene or in two different genes. Also called cis-trans test.
Complete dominance
The condition in which an allele is phenotypically expressed when one or both copies are present, so that the phenotype of the heterozygote is essentially indistinguishable from that of the homozygote.
Complete medium
For a microorganism, a medium that supplies all the ingredients required for growth and reproduction, including those normally produced by the wild-type organism.
Complete recessiveness
The condition in which an allele is phenotypically expressed only when two copies are present.
Conditional mutation
A mutation that results in a wild-type phenotype under one set of conditions but a mutant phenotype under other conditions. Temperature-sensitive mutations are a common type of conditional mutation.
Conjugation
In bacteria, process of unidirectional transfer of genetic material through direct cellular contact between a donor (“male”) cell and a recipient (“female”) cell.
Consensus sequence
The series of nucleotides found most frequently at each position in a particular DNA sequence among different species.
Conservative model
A model for DNA replication in which the two parental strands of DNA remain together and serve as a template for the synthesis of a new daughter double helix. The results of the Meselson–Stahl experiment did not support this model.
Constitutive gene
A gene whose expression is unregulated. The products of constitutive genes are essential to the normal functioning of the cell and are always produced in growing cells regardless of the environmental conditions.
Constitutive heterochromatin
Condensed chromatin that is always transcriptionally inactive and is found at homologous sites on chromosome pairs.
Contributing allele
An allele that affects the phenotype of a quantitative trait.
Coordinate induction
The simultaneous transcription and translation of two or more genes brought about by the action of an inducer.
Core enzyme
The portion of E. coli RNA polymerase that is the active enzyme; it is bound to the sigma factor, which directs the enzyme to the promoter region of genes.
Corepressor
In eukaryotes, a large multiprotein complex that interacts with repressors bound at enhancers, general transcription factors bound near the promoter, and RNA polymerase II. These interactions help inhibit transcription of regulated genes.
Core promoter
In eukaryotic genomes, the gene regulatory elements closest to the transcription start site that are required for RNA synthesis to begin at the correct nucleotide.
Correlation coefficient
A statistical measure of the strength of the association between two variables. See also regression.
Cotransduction
The simultaneous transduction of two or more bacterial genes, a good indication that the bacterial genes are closely linked.
Coupling
In individuals heterozygous at two genetic loci, the arrangement in which the wild-type alleles of both genes are on one homologous chromosome and the recessive mutant alleles are on the other; also called cis configuration.
Covariance
A statistical measure of the tendency for two variables to vary together; used to calculate the correlation coefficient between the two variables.
CpG island
DNA region containing many copies of the dinucleotide CpG. Many genes in eukaryotic DNA have CpG islands in or near the promoter. Methylation of the cytosines (C) in these islands represses transcription.
Crisscross inheritance
Transmission of a gene from a male parent to a female child to a male grandchild.
Cross
The fusion of male gametes from one individual and female gametes from another.
Cross-fertilization
The fusion of male gametes from one individual and female gametes from another.
Crossing-over
The process of reciprocal chromosomal interchange that occurs frequently during meiosis and gives rise to recombinant chromosomes.
C-value
The amount of DNA found in the haploid set of chromosomes.
Cyclin
Any of a group of proteins whose concentrations increase and decrease in a regular pattern through the cell cycle. The cyclins act in conjunction with cyclindependent kinases to regulate cell-cycle progression.
Cyclin-dependent kinase (Cdk)
Any of a group of protein kinases, activated by binding of specific cyclins, that regulate cell-cycle progression.
Cytokinesis
Division of the cytoplasm following mitosis or meiosis I and II during which the two new nuclei compartmentalize into separate daughter cells.
Cytosine (C) A pyrimidine
found in RNA and DNA. In doublestranded DNA, cytosine pairs with guanine, a purine, by hydrogen bonding.
