Chimeric selectable marker gene - a gene that is constructed from parts of two or more different genes and allows the host cell to survive under conditions where it would otherwise die.

Chitinase - an enzyme which breaks down chitin.

Chloramphenicol - an antibiotic that interferes with protein synthesis.

Chlorenchyma - tissue containing chloroplasts, including leaf mesophyll and other parenchyma cells.

Chlorophyll - one of the two pigments responsible for the green colour of most plants It is essential in the absorption of light energy for photosynthesis.

Chloroplast - specialised cytoplasmic organelle that contains chlorophyll Lens-shaped and bounded by a double membrane, chloroplasts contain membranous structures (thylakoids) piled up into stacks, surrounded by a gel-like matrix (stroma) They are the site of solar energy transfer and important reactions of starch or sugar synthesis Chloroplasts have their own DNA and are inherited cytoplasmi cally, independent of nuclear genes.

Chlorosis - failure of chlorophyll development, and appearance of yellow colour in plants, because of a nutritional disturbance or because of an infeccion by a virus, bacteria or fungus.

Chromatid - each of the two daughter strands comprising a duplicated chromosome The term remains in use while the two chromatids are still joined at the centromere As soon as the centromere divides, setting the two chromatids adrift (during anaphase of mitosis; and during anaphase II of meiosis), they are called chromosomes.

Chromatin - substance of which eukaryotic chromosomes are composed It consists of primarily DNAm with some proteins (mainly histones), and small amounts of RNA Originally named because of the readiness with which it stains with certain dyes (chromaticity).

Chromatin fibres - a basic organisational unit of eukaryotic chromosomes, consisting of DNA and associated proteins assembled into strands of 30 nm average diameter.

Chromatography - 1 a method for separating and identifying the components of mixtures of molecules having similar chemical and physical properties.
2 the term originally used by Mikhail Tswett (1906) to describe the separation of a mixture of leaf pigments on a calcium carbonate column.

Chromocentre - body produced by fusion of the heterochromatic regions of the chromosomes in the polytene tissues (eg, the salivary glands) of certain Diptera.

Chromogenic substrate - a compound or substance that contains a colour-forming group.

Chromomeres - small bodies, described by J Belling, that are identified by their characteristic size and linear arrangement along a chromosome.

Chromonema - sn optically single thread forming an axial structure within each chromosome.

Chromoplast - plastid containing pigments, such a chloroplast, or one in which carotenoids predominate.

Chromosomal aberration - any change in chromosome structure or number Although it can be a mechanism for enhancing genetic diversity, such alterations are usually fatal or ill-adaptive, especially in animals.

Chromosomal integration site - a chromosomal location where foreign DNA can be integrated, often without impairing any essential function in the host organism.

Chromosomal polymorphism - the occurrence of one to several chromosomes in two or more alternative structural forms within a population; the structurally changed chromosomes are the result of chromosome mutations (ie, any structural change involving the gain, loss or re-location of chromosome segments).

Chromosome - 1a single DNA molecule, a tightly coiled strand of DNA, condensed into a compact structure in vivo by complexing with accessory histones or histone-like proteins.
2a group of nuclear bodies containing genes which are largely responsible for the differentiation and activity of a eukaryotic cell; one of the bodies into which the nucleus resolves itself at the beginning of mitosis and from which it is derived at the end of mitosis Chromosomes contain most of the cell's DNA Chromosomes exist in pairs in eukaryotes - one paternal (from the male parent) and one maternal (from the female parent) Each eukaryotic species has a characteristic number of chromosomes Bacterial and viral cells contain only a single chromosome, consisting of a single or double strand of DNA or, in some viruses, RNA, without histones.

Chromosome aberration - abnormal structure or number of chromosomes; includes deficiency, duplication, inversion, translocation, aneuploidy, polyploidy, or any other change om the normal pattern.

Chromosome banding - staining of chromosomes in such a way that light and dark areas occur along the length of the chromosomes in repeatable patterns Lateral comparisons identify pairs Each chromosome can be identified by its banding pattern.

Chromosome jumping - a technique that allows two segments of duplex DNA that are separated by thousands of base pairs (about 200 kb) to be cloned together After sub-cloning, each segment can be used as a probe to identify cloned DNA sequences that, at the chromosome level, are roughly 200 kb apart.