Co inearity - a relationship in which the units in one molecule occur in the same sequence as the units in another molecule which they specify; eg, the nucleotides in a gene are co-linear with the amino acids in the polypeptide encoded by that gene.

Collenchyma - derived from parenchyma and denoting a type of cell tissue A tissue of living cells, the walls being unevenly thickened with cellulose and hemicellulose, but never lignified; it functions in mechanical support in young, short lived or non woody organs and is thus found in midribs and leaf petioles.

Colony - 1 an aggregate of identical cells (clones) derived from a single progenitor cell.
2 a group of interdependent cells or organisms.

Colony hybridisation - a technique that uses a nucleic acid probe to identify a bacterial colony with a vector carrying a specific cloned gene or genes.

Combinatorial library - during the ligation reaction with cDNAs of light and heavy antibody chains into a bacteriophage lambda (1) vector, many novel combinations consisting of one heavy and one light chain coding region are formed The library comprises these combinations, each in a separate vector.

Commensalism - the interaction of two or more dissimilar organisms where the association is advantageous to one without affecting the other(s) cf parasitism; symbiosis.

Companion cell - living cell associated with the sieve cell of phloem tissue in vascular plants.

Comparative gene mapping - the comparison of map locations of genes between species The results of these comparisons indicate substantial conservation of blocks of genes and even large segments of chromosomes between species Great use can be made of this conservation of map position For example, in the case of mammals, it means that if a gene has been mapped in one or both of the intensely-mapped species (humans and mice), then the likely location of that gene in other mammals can be predicted with considerable confidence Conversely, if a mapped anonymous DNA marker has an effect on a quantitative trait (this being indicative of the marker being linked to a quantitative trait locus (QTL)) in, say, cattle, then knowledge of the comparative map between cattle and humans can identify genes in the homologous region of the human genome that could correspond to the QTL Such genes are called comparative positional candidate genes (qv).

Comparative positional candidate gene - a gene that is likely to be located in the same region as a DNA marker that has been shown to be linked to a single locus trait or to a quantitative trait locus (QTL), where the gene's likely location in the genome of the species in question is based on its known location in the map of another species, ie, is based on the comparative map between the two species.

Competence - ability of a bacterial cell to take up DNA molecules and become genetically transformed.

Competency - an ephemeral state, induced by treatment with cold cations, during which bacterial cells are capable of taking up foreign DNA.

Competent - a competent cell is capable of developing into a fully functional embryo The opposite is non competent.

Complement proteins - proteins that bind to antibodyantigen complexes and help degrade the complexes by proteolysis.

Complementarity - the relationship between the two strands of a double helix of DNA Thymine in one strand pairs with adenine in the other strand, and cytosine in one strand pairs with guanine in the other strand.

Complementary entity - 1 one of a pair of nucleotide bases that form hydrogen bonds with each other Adenine (A) pairs with thymine (T) [or with Uracil (U) in RNA], and guanine (G) pairs with cytosine (C).
2 one of a pair of segments or strands of nucleic acid that will hydridise (join by hydrogen bonding) with each other.

Complementary genes - two or more interdependent genes, such that (in the case of dominant complementarity) the dominant allele from either gene can only produce an effect on the phenotype of an organism if the dominant allele from the other gene is also present; or (in the case of recessive complementarity) only double homozygous recessive show the effect.

Complementary homopolymeric tailing - the process of adding complementary nucleotide extensions to different DNA molecules, eg, dG (deoxyguanosine) to the 3'-hydroxyl ends of one DNA molecule and dC (deoxycytidine) to the 3'-hydroxyl ends of another DNA molecule to facilitate, after mixing, the joining of the two DNA molecules by base pairing between the complementary extensions Also called dG - dC tailing, dA - dT tailing.

Complementary nucleotides - members of the pairs adenine-thymine, adenineuracil, and guanine-cytosine that have the ability to hydrogen bond to one another.

Complementation test - introduction of two mutant chromosomes into the same cell to determine whether the mutants are alleles of the same gene If the mutations are non-allelic, the genotype will be m1 +/+ M2 , and the phenotype will be wild-type (normal), because each chromosome covers for the other In contrast, if they are allelic, the mutant phenotype will result.

Complete digest - the treatment of a DNA preparation with an endonuclease for sufficient time for all of the potential target sites within that DNA to have been cleaved cf partial digest.

Composite transposon - a transposable element formed when two identical or nearly identical transposons insert on either side of a nontransposable segment of: DNA, such as the bacterial transposon Tn5/.