D

Data warehouse

A collection of databases, data tables, and mechanisms to access the data on a single subject.

Deletion

A loss of part of the DNA from a chromosome; can lead to a disease or abnormality.

See also: chromosome, mutation

Deletion map

A description of a specific chromosome that uses defined mutations --specific deleted areas in the genome-- as 'biochemical signposts,' or markers for specific areas.

Deoxyribonucleotide

See: nucleotide

Deoxyribose

A type of sugar that is one component of DNA (deoxyribonucleic acid).

Diploid

A full set of genetic material consisting of paired chromosomes, one from each parental set. Most animal cells except the gametes have a diploid set of chromosomes. The diploid human genome has 46 chromosomes.

See also: haploid

Directed evolution

A laboratory process used on isolated molecules or microbes to cause mutations and identify subsequent adaptations to novel environments.

Directed mutagenesis

Alteration of DNA at a specific site and its reinsertion into an organism to study any effects of the change.

Directed sequencing

Successively sequencing DNA from adjacent stretches of chromosome.

Disease-associated genes

Alleles carrying particular DNA sequences associated with the presence of disease.

DNA (deoxyribonucleic acid)

The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases adenine (A), guanine (G), cytosine (C), and thymine (T). In nature, base pairs form only between A and T and between G and C; thus the base sequence of each single strand can be deduced from that of its partner.

DNA bank

A service that stores DNA extracted from blood samples or other human tissue.

DNA probe

See: probe

DNA repair genes

Genes encoding proteins that correct errors in DNA sequencing.

DNA replication

The use of existing DNA as a template for the synthesis of new DNA strands. In humans and other eukaryotes, replication occurs in the cell nucleus.

DNA sequence

The relative order of base pairs, whether in a DNA fragment, gene, chromosome, or an entire genome.

See also: base sequence analysis

Domain

A discrete portion of a protein with its own function. The combination of domains in a single protein determines its overall function.

Dominant

An allele that is almost always expressed, even if only one copy is present.

See also: gene, genome

Double helix

The twisted-ladder shape that two linear strands of DNA assume when complementary nucleotides on opposing strands bond together.

Draft sequence

The sequence generated by the HGP as of June 2000 that, while incomplete, offers a virtual road map to an estimated 95% of all human genes. Draft sequence data are mostly in the form of 10,000 base pair-sized fragments whose approximate chromosomal locations are known.

See also: sequencing, finished DNA sequence, working draft DNA sequence

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E

Electrophoresis

A method of separating large molecules (such as DNA fragments or proteins) from a mixture of similar molecules. An electric current is passed through a medium containing the mixture, and each kind of molecule travels through the medium at a different rate, depending on its electrical charge and size. Agarose and acrylamide gels are the media commonly used for electrophoresis of proteins and nucleic acids.

Electroporation

A process using high-voltage current to make cell membranes permeable to allow the introduction of new DNA; commonly used in recombinant DNA technology.

See also: transfection

Embryonic stem (ES) cells

An embryonic cell that can replicate indefinitely, transform into other types of cells, and serve as a continuous source of new cells.

Endonuclease

See: restriction enzyme

Enzyme

A protein that acts as a catalyst, speeding the rate at which a biochemical reaction proceeds but not altering the direction or nature of the reaction.

Epistasis

One gene interfers with or prevents the expression of another gene located at a different locus.

Escherichia coli

Common bacterium that has been studied intensively by geneticists because of its small genome size, normal lack of pathogenicity, and ease of growth in the laboratory.

Eugenics

The study of improving a species by artificial selection; usually refers to the selective breeding of humans.

Eukaryote

Cell or organism with membrane-bound, structurally discrete nucleus and other well-developed subcellular compartments. Eukaryotes include all organisms except viruses, bacteria, and bluegreen algae.

See also: prokaryote, chromosome.

Evolutionarily conserved

See: conserved sequence

Exogenous DNA

DNA originating outside an organism that has been introducted

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