Plasmid
Small circular DNA replicating independently of the chromosome in bacteria and unicellular eukaryotes (e.g. yeasts). Plasmids usually carry genes for e.g. antibiotic resistance, colicin production and are widely used in genetic engineering as vectors. Vectors are vehicles into which foreign genes are inserted for subsequent cloning or expression in bacterial cells.
Point mutation
In molecular genetics, a point mutation is caused by the substitution of one nucleotide for another. In classical genetics, point mutation refers to any mutation that is not associated with a cytologically detectable chromosomal aberration or one that has no effect on crossing over.
Polygeny
Most diseases are polygenic, i.e. caused by the interplay of several genes.
Polymorphism
In classical population genetics, polymorphism refers to the coexistance of different alleles in a population/species at significant frequencies (the most frequent allele should be less than 95%%). However, the term polymorphism is frequently used simply to indicate that genetic variation occurs within a certain part of the genome. In extreme, polymorphism can refer to just one nucleotide, e.g., SNP.
Primer walking
Sequencing method in which the sequence data of the sequenced section are exploited to synthesize the following primer. Starting from the first priming site this continues until the DNA template has been sequenced completely.

Principal component analysis
Visual and numerical analysis of collinearity among variables. Allows for the mapping of high-dimensional data to a lower dimension for visualisation, analysis and modelling.
Probe
In general, probe refers to any biochemical/nucleic acid/oligo etc. labelled with radioactive isotopes or tagged in other ways for identification. A probe is used to identify or isolate a gene, its product, or a protein. In microarrays, the probe is immobilised in regular arrangement on the substrate.
Protein arrays
Arrays consisting of proteins themselves or of probes used for capturing proteins.
Pseudogene
Stretch of DNA related in sequence to a funtional gene; it is however inactive as a result of the changes it has accumulated during evolution.

Radioimmunoassay
= RIA: very sensitive diagnostic test using radioactively labeled specific antibodies or antigens to detect trace amounts of substances.

Reader
Synonym for microarray scanner; after fluorescent labelling and hybridisation, the reader scans the microarrays into a computer for subsequent analysis.

Regulatory sequence
A DNA sequence involved in regulating the expression of structural genes in the common operon. These stretches of DNA might be attenuators, operators, or promoters.

RT-PCR
Reverse Transcriptase Polymerase Chain Reaction: The mRNA is first reverse-transcribed into cDNA, and the cDNA is then amplified to measurable levels using PCR. PCR primers for all genes of interest are required.

Scanner
Also referred to as "reader"; after fluorescent labelling and hybridisation, the scanner or reader scans the microarrays into a computer for subsequent analysis.

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