Nick translation
Refers to the in vitro procedure used to radioactively label DNA uniformly to a high specific activity. Nicks are introduced into the unlabelled DNA by an endonuclease, thus creating 3' hydroxyl termini. E. coli DNA polymerase then adds radioactive residues to the 3' hydroxy terminus of the nick; nucleotides are removed from the 5' side. This procedure leads to an identical DNA molecule with the nick located further along the duplex.
Nucleotide
Monomeric units from which DNA or RNA polymers are constructed. They consist of a purine or pyrimidine base, a pentose, and a phosphoric acid group. The nucleotides of DNA are deoxyadenylic acid, thymidylic acid, deoxyguanilic acid, and deoxycytidylic acid. Those of RNA are adenylic acid, uridylic acid, guanylic acid and cytidylic acid.
Oligonucleotide chips
Oligonucleotide chips consist of small glass plates with thousands of short 20-mer oligonucleotide probes attached to their surface. The oligos are synthesized directly onto the surface using a combination of semiconductor-based photolithography and light-directed chemical synthesis. Very large numbers can be probed; at present chips contain over 65,000 probes.
Operon
A unit that consists of one of more cistrons which function coordinateley under the control of an operator gene.
ORF
Open Reading Frame; a reading frame refers to a nucleotide sequence that starts with an initiation codon, partitions the subsequent nucleotides into amino-acid-encoding triplets and ends with a termination codon. The interval between the start and stop codons is referred to as the open reading frame.
PCR
Polymerase chain reaction. This is an in vitro technique for the selective amplification of defined nucleic acid regions in a DNA mixture by copying the complementary strands of a target DNA molecule simultaneously for a series of cycles until the desired amount is obtained. The principle: Primers are synthesised which have nucleotide sequences complementary to the DNA that flanks the target region. Then, the DNA is heated to separate the complementary DNA strands and cooled to allow the primers to bind to the flanking sequences. Heat-stable DNA (Taq) is added and the reaction allowed to proceed for a series of replication cyles. Twenty cycles will render an approximately millionfold amplification of the soruce DNA.
Penetrance
Defined as the ratio of individuals who have a disease-causing allele and manifest the disease versus those who have this disease causing allele but do not manifest the associated disease. Diseases are usually associated with either high penetrance or low penetrance alleles.
Peptide
Two or more amino acids are joined by a so-called peptide-bond.

Phenotype
Observable properties of an organism produced by the genotype in conjunction with the environment.

Photolithography
Selective masking generates light patterns that direct chemical transformations to specific areas of photosensitive surfaces. Photolithography usually requires expensive equipment and particular knowledge; the technology is protected by patents

Physical map
Map of the linear order of genes on a chromosome with units that indicate their distances determined by methods other than genetic recombination. These include e.g. nucleotide sequencing, electon micrographs of heteroduplex DNAs, etc.)

Piezoelectric
Becoming electrically polarised when subject to the mechanical stress; quartz for example produces an electric charge when squeezed.

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