Impeller
An agitator used for mixing the contents of a bioreactor.

Impermeable junction
A cell-cell junctional complex that connects cells together in such  a way that even small molecules cannot diffuse between the cells. These are also called tight junctions.

Importin
A protein that binds to a ‘cargo protein’ in the cytoplasm and transports it into the nucleus through a nuclear pore complex. The importin returns to the cytoplasm with the help of Ran, a member of the GTPase superfamily.

Imprinting
A change in a gene during passage throught a sperm or egg that results in the paternal and maternal alleles having different properties in the very early embryo. This may be brought about by methylation of DNA.

In-phase exons
Exons that begin and end at the same position with respect to codon boundaries and the flanking introns have the same phase. These exons can undergo unlimited duplications and participate in exon shuffling because they do not disturb the overall reading frame.

In silico (biology)
(Lit. computer mediated). The use of computers to simulate, process, or analyse a biological experiment.

In silico transcriptomics
A novel method of EST database screening that allows new potential tumour-associated genes to be efficiently selected. It is a complementary approach to experimental tumour antigen discovery.

In situ
(L. in place). In its normal position; restricted to the site of origin. Assays or manipulations performed with intact cells or tissues. Usually refers to an intact tissue as opposed to a biochemical extract.

In situ colony; in situ plaque hybridisation
A method of screening for the presence of specific DNA sequences by the hybridisation of nucleic acid probes to the DNA molecules present in colonies or plaques growing on plates or membranes.

In situ hybridisation
1. A type of hybridisation in which the immobilised target is part of a whole chromosome or cell. 2. Use of DNA or RNA probe to detect the presence of a complementary sequence in cloned bacterial or eukaryotic cells in culture.

In situ PCR
An RT-PCR reaction used for amplification of mRNA in its natural location in the cell allowing exact localization of even scarce transcripts. This method is more sensitive than those based on hybridisation.

In situ plaque hybridisation
See in situ colony.

In vitro
Literally in glass, i.e., in an artificial environment as in a test tube. Outside the living organism.

In vitro complementation assay
A test for identifying the component of a wild type cell that can confer activity on an extract made from a mutant cell. The assay is based on identifying the component that renders the mutation inactive.

In vitro embryo production (IVEP) The combination of ovum pickup, in vitro maturation of ova, and in vitro fertilisation. This method helps to overcome the variability between donors in the number of ova collected in embryo-transfer programmes.

In vitro fertilisation (IVF)
A technique by which the egg is fertilised with sperm outside the body. The egg fertilised in this manner is cultured outside the body for a few days (in order to confirm the success of feertilisation) before reimplantation into a female recipient.

In vitro maturation (IVM)
Culture of immature ova in the laboratory until they are ready for in vitro fertilisation.

In vitro mutagenesis
See directed mutagenesis.

In vitro packaging
The assembly of bacteriophage particles in vitro by mixing DNA with cell extracts containing bacteriophage heads, tails and enzymes required for packaging.

In vitro transcription; cell-free transcription
The synthesis of RNA in the test tube using purified DNA preparations as a template. For E. coli, “coupled systems” are available which carry out both mRNA synthesis and its translation into protein. For eukaryotes, separate cell-free systems have to be set up for this purpose because there are three functionally distinct RNA polymerase complexes.

In vitro translation
Protein synthesis directed by either purified DNA with bacterial extracts or mRNA with wheat germ synthesis factors. The reaction mixture is often supplemented with ATP, GTP and amino acids.

In vivo
Within the living system.

In vivo gene therapy
The delivery of a functional gene(s) into somatic tissues to treat a genetic disease.

Inactivated agent
An organism such as a virus or a bacterium that has been treated to prevent it from causing a disease.

Inactivated vaccine
Vaccine composed of killed pathogen.