Cell

The basic unit of any living organism that carries on the biochemical processes of life.

See also: genome, nucleus

Centimorgan (cM)

A unit of measure of recombination frequency. One centimorgan is equal to a 1% chance that a marker at one genetic locus will be separated from a marker at a second locus due to crossing over in a single generation. In human beings, one centimorgan is equivalent, on average, to one million base pairs.

See also: megabase

Centromere

A specialized chromosome region to which spindle fibers attach during cell division.

Chimera (pl. chimaera)

An organism that contains cells or tissues with a different genotype. These can be mutated cells of the host organism or cells from a different organism or species.

Chimeraplasty

An experimental targeted repair process in which a desirable sequence of DNA is combined with RNA to form a chimeraplast. These molecules bind selectively to the target DNA. Once bound, the chimeraplast activates a naturally occurring gene-correcting mechanism. Does not use viral or other conventional gene-delivery vectors.

See also: gene therapy, cloning vector

Chloroplast chromosome

Circular DNA found in the photosynthesizing organelle (chloroplast) of plants instead of the cell nucleus where most genetic material is located.

Chromomere

One of the serially aligned beads or granules of a eukaryotic chromosome, resulting from local coiling of a continuous DNA thread.

Chromosomal deletion

The loss of part of a chromosome's DNA.

Chromosomal inversion

Chromosome segments that have been turned 180 degrees. The gene sequence for the segment is reversed with respect to the rest of the chromosome.

Chromosome

The self-replicating genetic structure of cells containing the cellular DNA that bears in its nucleotide sequence the linear array of genes. In prokaryotes, chromosomal DNA is circular, and the entire genome is carried on one chromosome. Eukaryotic genomes consist of a number of chromosomes whose DNA is associated with different kinds of proteins.

Chromosome painting

Attachment of certain fluorescent dyes to targeted parts of the chromosome. Used as a diagnositic for particular diseases, e.g. types of leukemia.

Chromosome region p

A designation for the short arm of a chromosome.

Chromosome region q

A designation for the long arm of a chromosome.

Clone

An exact copy made of biological material such as a DNA segment (e.g., a gene or other region), a whole cell, or a complete organism.

Clone bank

See: genomic library

Cloning

Using specialized DNA technology to produce multiple, exact copies of a single gene or other segment of DNA to obtain enough material for further study. This process, used by researchers in the Human Genome Project, is referred to as cloning DNA. The resulting cloned (copied) collections of DNA molecules are called clone libraries. A second type of cloning exploits the natural process of cell division to make many copies of an entire cell. The genetic makeup of these cloned cells, called a cell line, is identical to the original cell. A third type of cloning produces complete, genetically identical animals such as the famous Scottish sheep, Dolly.

See also: cloning vector

Cloning vector

DNA molecule originating from a virus, a plasmid, or the cell of a higher organism into which another DNA fragment of appropriate size can be integrated without loss of the vector's capacity for self-replication; vectors introduce foreign DNA into host cells, where the DNA can be reproduced in large quantities. Examples are plasmids, cosmids, and yeast artificial chromosomes; vectors are often recombinant molecules containing DNA sequences from several sources.

Code

See: genetic code

Codominance

Situation in which two different alleles for a genetic trait are both expressed.

See also: autosomal dominant, recessive gene

Codon

See: genetic code

Coisogenic or congenic

Nearly identical strains of an organism; they vary at only a single locus.

Comparative genomics

The study of human genetics by comparisons with model organisms such as mice, the fruit fly, and the bacterium E. coli.

Complementary DNA (cDNA)

DNA that is synthesized in the laboratory from a messenger RNA template.

Complementary sequence

Nucleic acid base sequence that can form a double-stranded structure with another DNA fragment by following base-pairing rules (A pairs with T and C with G). The complementary sequence to GTAC for example, is CATG.

Complex trait

Trait that has a genetic component that does not follow strict Mendelian inheritance. May involve the interaction of two or more genes or gene-environment interactions.

See also: Mendelian inheritance, additive genetic effects

Computational biology

See: bioinformatics

Confidentiality

In genetics, the expectation that genetic material and the information gained from testing that material will not be available without the donor's consent.

Congenital

Any trait present at birth, whether the result of a genetic or nongenetic factor.

See also: birth defect

Conserved sequence

A base sequence in a DNA molecule (or an amino acid sequence in a protein) that has remained essentially unchanged throughout evolution.

Constitutive ablation

Gene expression that results in cell death.

Contig

Group of cloned (copied) pieces of DNA representing overlapping regions of a particular chromosome.

Contig map

A map depicting the relative order of a linked library of overlapping clones representing a complete chromosomal segment.

Cosmid

Artificially constructed cloning vector containing the cos gene of phage lambda. Cosmids can be packaged in lambda phage particles for infection into E. coli; this permits cloning of larger DNA fragments (up to 45kb) than can be introduced into bacterial hosts in plasmid vectors.

Crossing over

The breaking during meiosis of one maternal and one paternal chromosome, the exchange of corresponding sections of DNA, and the rejoining of the chromosomes. This process can result in an exchange of alleles between chromosomes.

See also: recombination

Cytogenetics

The study of the physical appearance of chromosomes.

See also: karyotype

Cytological band

An area of the chromosome that stains differently from areas around it.

See also: cytological map

Cytological map

A type of chromosome map whereby genes are located on the basis of cytological findings obtained with the aid of chromosome mutations.

Cytoplasmic (uniparental) inheritanc

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