I

Idiotope:

Epitopes present in the unique variable sequences of an immunoglobulin molecule. These may or may not coincide with the immunoglobulin's paratope.

Immunoprecipitation:

A process whereby a particular protein of interest is isolated by the addition of a specific antibody, followed by centrifugation to pellet the resulting immune complexes. Often, staphylococcal proteins A or G, bound to sepharose or some other type of macroscopic particle, is added to the reaction mix to increase the size and ease collection of the complexes. Usually, the precipitated protein is subsequently examined by SDS-PAGE.

Imprinting:

It describes a change in a gene that occurs during the passage through the sperm or the egg with the result that the paternal and the maternal alleles have different properties in the very early embryo.

Indirect End Labelling:

It is a technique for examining the organization of DNA by making a cut at a specific site and isolating all the fragments containing the sequence adjacent to one side of the cut.

Inducer:

A small molecule, such as IPTG, that triggers gene transcription by binding to a regulator protein, such as LacZ.

Informatics:

The study of the application of computer and statistical techniques to the management of information. In genome projects, informatics includes the development of methods to search databases quickly, to analyze DNA sequence information, and to predict protein sequence and structure from DNA sequence data.

Initiation Codon:

The codon at which translation of a polypeptide chain is initiated. This is usually the first AUG triplet in the mRNA molecule from the 5' end, where the ribosome binds to the cap and begins to scan in a 3' direction. However, the surrounding sequence context is important and may lead to the first AUG being bypassed by the scanning ribosome in favor of an alternative, downstream AUG. Also called a "start codon". Occasionally other codons may serve as initiation codons, e.g. UUG.

Initiator tRNA:

A special tRNA responsible for annealing to the start codon, in the P site of the ribosome, to initiate polypeptide synthesis.

Insert:

In a complete plasmid clone, there are two types of DNA - the "vector" sequences and the "insert". The vector sequences are those regions necessary for propagation, antibiotic resistance, and all those mundane functions necessary for useful cloning. In contrast, however, the insert is the piece of DNA in which you are really interested.

Insertion:

The presence of additional bases within a sequence that are not present in wild-type sequence.

Insertion Sequence:

A small bacterial transposon carrying only the genetic functions involved in transposition. There are usually inverted repeats at the ends of the insertion sequence.

In Situ Hybridization:

Use of a DNA or RNA probe to detect the presence of the complementary DNA sequence in cloned bacterial or cultured eukaryotic cells.

Internal Positive Control (IPC):

An exogenous IPC can be added to a multiplex assay or run on its own to monitor the presence of inhibitors in the template. Most commonly the IPC is added to the PCR master mix to determine whether inhibitory substances are present in the mix. Alternatively, it can be added at the point of specimen collection or prior to nucleic acid extraction to monitor sample stability and extraction efficiency, respectively.

Intercistronic Region:

It is the distance between the termination codon of one gene and the initiation codon of the next gene.

Intergenic:

Between two genes.

Interphase:

The period in the cell cycle when DNA is replicated in the nucleus; followed by mitosis.

Intron:

Introns are portions of genomic DNA which are transcribed (and thus present in the primary transcript) but which are later spliced out. They thus are not present in the mature mRNA.

Inverse PCR:

Variation of PCR that makes the amplification of DNA segments of unknown sequence that flank DNA segments of known sequence possible; in brief, total DNA is digested to completion and fragments ligated under conditions that favour circularization of fragments; pair of PCR primers, designed from known sequence known sequence, are used to prime PCR from opposite strands resulting in amplification of fragment of unknown sequence.

Inverted Repeats:

Two copies of the same or related sequence of DNA repeated in opposite orientation on the same molecule.

In Vitro:

Growth in any type of culture vessel; Outside a living organism.

In Vivo:

In living organism.